MSD Ignition or Weber Carb Issue?

[David Briggs]

Carbs Unlimited sells a very complete setup, comes with the Synchronizing tool and a book, lingage, everything. There are different manifolds available, the best being the newest, a manifold that has a plenum chamber for vacuum to operate power brakes and a PVC system.
As far as knowledge, Ingelese is probably the best and easiest to understand of the Weber Gurus out there.
Dave
Dave

 

[Chuck]

Scott:

Very nice idea. Had not seen those before. I have covers over the trumpts only so the air coming in the idle port would still be unfiltered, but I am guessing that by elevating the point where the air enters would still reduce the risk of sediment getting in the opening.

Thanks for the tip.

 

[Ian Clark]

Hi Chuck,

A couple of things come to mind on your driveability issues. After cleaning and fresh start up it runs almost great for a half hour or so then goes off. Doesn't restart running as well either... hmmmmm.

Do you have a heat sheild around the carbs? In low speed around town driving the back two carb bodies can get up to 160f, close to the boiling point of gasoline. That can lead to bad restarts or carb fires in worst case scenarios.

The idle speed screws are moving due to vibration or heat expansion. The screws on the idle stops are spring loaded but can still move. Try taking them out, clean with carb cleaner then give the threads a light coat of red loctite. DO NOT REINSTALL the screws untill the locktite has air dried, probably 24hrs. This seems to stop migration of the screws from proper settings.

The linkages have an at rest amount of play, an under tension length which is affected by the at rest play. This can really mess up your off idle throttle responce and contributes to simultaneous popping in the carbs and backfires.

These at rest and loaded linkage lengths also affect carb syncronization, so you may not be as close to balanced as thought. You could have a bank to bank out of sync that doesn't show up on idle with the syncrometer because the cross linkages are not openning the banks of carbs equally.

Without a chassis dyno it takes a lot of test drives and inspections of plugs and exhaust temperatures to get a read on the carbs. Also knowing the carbs are machanically balanced is hard to do because there's no load on the engine when your going for matched airflow at 2,000rpm.

Once you get this worked out, the fluid broad power band and sound of these carbs will make it all worthwhile Hope this helps.

Cheers

 

[Chuck]

Ian:

Just when I thought I was starting to figure out these Webers you introduce a whole new set of issues!!!

Good thoughts and appreciate the suggestions.

Time permitting, hope to approach this methodically: pop the tops off the carbs. check for any sediment, adjust the floats, etc.

Next step will be the adjustments you have suggested if it is not a dirt issue.

Should point out that the recent carb tuning done to date has been with a thoroughly warmed engine driven at least 8 miles before checking for syncronization and idle mixture.

Time permitting, should know something in a few days.

 

[Chuck]

Did some more carb tinkering Saturday. I am not so sure it is a dirt or dust issue as noted previously.

Once again it ran reasonably well until it was warmed up - say about twenty minutes into our ride. Pops at cruise speed were few at startup, then minimal. Then it started popping intermittantly at cruise speed, be it 2000 rpm or 3000 rpm. You can feel the engine missing when it pops - it is subtle but there.

I accellerates fine.

Stopped the car and found a carb that was not firing. Put the syncro meter on and found it was flowing slightly less air. Slight adjustment and it was firing. Now with all four carbs balanced perfectly per the meter, took it for another ride.

Same issue. Popping intermittanly at cruise speed and low speed. Yet it idles smoothly with no popping or backfiring, even thought he mixture screws are not calibrated.

I can't get the mixture screws adjusted. Most will reach the point where the idle speed drops while turning them in, but usually 2 or 3 carbs (it changes from carb to carb depening on the day of week) won't respond. I can turn in the mixture screw all the way and it makes NO difference in idle speed on those offending carbs. Obviously there is an issue. I have changed the idle jets, from 55 to 60 and back to 55. No siginficant difference.

So not being able to even get the idle mixture screws to respond, trying to fiddle with jets seems premature.

Ian, your point regarding balance of the carb as higher speeds is well taken. But how does one check balance at 3000 or 4000 rpm? Sure can't do it with that little flow meter! I guess pulling plugs is about the only way. But then what does one do? Adjust the flow to get it better at higher RPMs? That would then throw it off at idle, and then we get back to not having a cylinder fire at idle.

I am wondering if perhaps it is too rich. When cold that extra fuel is good, but when hot it is not. But we are already down to a 55 idle jet from 60 so . . . . . May be a larger air jet?

Despite the rising frustration level, still plan to pop the tops off the carbs check for sediment and recheck the float levels.

Oh and one other issue. For fifteen minutes after shut down one of the forward carbs spills gas into the throat of the carb. You can see the puddle of gas just setting on the throttle plate. It happens on just one throat of one carb, but today is Sunday and that could change tommarow.

I am just about ready to buy an Edelbrock intake manifold and a Holley carb. But Ryan does not want to give up yet . . . .

 

[Chuck]

Re: Weber Carb Issues

Idle stop screws.

Just thought of another issue.

Have seen two ways for setting up the idle on Webers:

1. Use the idle stop screw on ONE carb only. Remove the other four. Then adjust the linkage to get the flow equal.

2. Use the two idle stop screws on the carbs connected to the main linkage. Adjust those two stop screws for proper flow and then adjust the linkage to match those settings.

3. Keep all four idle stop screws, adjust for proper flow, and then adjust the linkage to match those settings.

The downside of using more than one stop screw is one may not precisely match the lnkage to the stop screw setting, it would seem to me.

Plus if more than one idle stop screw is kept in play, how would one finalize the idle speed adjustment? Adjust idle with more than one screw than recheck with the flow meter?

I am using number one. I wonder now if using number 2 might give more stable settings.

Throttle Springs.

All four carbs have throttle return springs. I have seen some sources recommend removing the springs from the two dependent carbs so only two return springs are used.

I have all four in place. Perhaps the extra tension contributes to unreliable alignment?

 

[Randy V]

Hi Chuck,

The spill-over can be caused by a couple of different things;

1) Float hanging up allowing for the float level to be too high

2) Fuel pressure too high. I would recommend turning pressure down to 2.5 PSI for now and if running at the track bring it up 1 PSI.

I'm sure Jac and others with far more Weber IDA/IDF experience will chime in on both of these..

I might also suggest that you double check the lash on your valves.
Valve lash will change cold to hot.
With Hydraulic lifters if you set to zero lash when cold, you're normally just fine.
With Solids I like to set them just a tad (.001-.002) looser than spec when cold.

I know it's easy for us arm-chair shop foremen to tell you what to do - but those are my best recommendations at this time..

 

[Mike Christian]

What worked best for me is a basic process - you can chase all kinds of variables, but you must rule some things out. First - you have to make sure the rest of the engine is set up correctly - valve adjustment, timing, air leaks in the intake and exhaust systemet. These carbs come last in the chain. Next - fuel pressure - these like it low (my experience was 2-3psi).

Next I disconnect the linkage on all carbs and set them to baseline - verify mixture screw profiles the same, mixture screws out one turn, idle jets clean, accel pump equal threads past the nuts, bypass screws shut, one turn in on the ide screws, start it and warm it up (it will sound like crap, but keep it running and warm it up). Once warm, pick a carb and balance the air flow between the barrels using the air bypass screw (bring the lower flowing carb up to the higher flowing carb by opening the lower barrel bypass screw slowly (you shouldn't have to open it to much). Repeat on all carbs one at a time. Now, the difference in readings between the different carb sets should be due to idle screw differences. You can try to get those matched closer by fine adjustments on the idle screws - just get the ones, if any that are far from the others. Now adjust the idle mixture screws - close one slowly until there is a slightly noticeable drop in rpm - play back and forth until you feel it (you should be +- 1/2 turn from the one turn out). Repeat this for each barrel. Check airflows again - they should still be the same and matched barrel to barrel at each carb and then with each carb nearly matched between carbs. As you do this process with the mixture screws the engine should start to smooth out as you get to the last carbs. So now you check airflows again - they should match on all barrels and all carbs. If they don't you have to tweak the idle screw and then the mixture screws to get them all breathing the same. Once this is done, then you connect the linkage and start it up again and check the airflows of all barrels and all carbs. Any changes are due to linkage. Adjust out any changes while connecting up your linkage. You should check the linkage at idle and at higher RPM to make sure all angles of the linkage are the same and everything is tracking. Now your carbs are synched. Go drive it.

If the engine pops at idle, then you have a blocked idle jet or too small of an idle jet.

If the engine pops on acceleration then check the accelertor pump squirt for more or less squirt depending on the symptom. If the car pops and hesitates above around 2500-3000 rpm or so through 4000-4500 RPM or so, then you main jet may need to be upped a size. Above 4500 your air correction jet needs to be looked at.

For me, following this systematic approach is the only way to rule things out as you go.

Keep working it - and please post your results....

 

[Mike Christian]

I am not so sure it is a dirt or dust issue as noted previously.

you found dirt in the jets, so there was an issue and may still be one.

Once again it ran reasonably well until it was warmed up - say about twenty minutes into our ride. Pops at cruise speed were few at startup, then minimal. Then it started popping intermittantly at cruise speed, be it 2000 rpm or 3000 rpm. You can feel the engine missing when it pops - it is subtle but there..

You need to check the carbs when it is warmed up - if you are doing it only when cold, then things can change when warm. Personally, I synch them with a warm engine. I drive with a warm engine so that is most important. My car runs a bit rough until warm - then it purrs.

I accellerates fine.

Then the accelerator pumps are probably set right.

Stopped the car and found a carb that was not firing. Put the syncro meter on and found it was flowing slightly less air. Slight adjustment and it was firing. Now with all four carbs balanced perfectly per the meter, took it for another ride.

Same issue. Popping intermittanly at cruise speed and low speed. Yet it idles smoothly with no popping or backfiring, even thought he mixture screws are not calibrated.

Until the carbs are near correctly adjusted - including the mixture screws, none of this matters really. What your engine is telling you is that you don't have it set up - it can be one of a few things here.

can't get the mixture screws adjusted. Most will reach the point where the idle speed drops while turning them in, but usually 2 or 3 carbs (it changes from carb to carb depening on the day of week) won't respond. I can turn in the mixture screw all the way and it makes NO difference in idle speed on those offending carbs. Obviously there is an issue. I have changed the idle jets, from 55 to 60 and back to 55. No siginficant difference.

So not being able to even get the idle mixture screws to respond, trying to fiddle with jets seems premature.

Yes, fiddling with idle jets seems premature here IMO...until you get your carbs closer together in settings (flow and mixture) it is hard to get a handle on what is changing what. You can chase your tail.

Ian, your point regarding balance of the carb as higher speeds is well taken. But how does one check balance at 3000 or 4000 rpm? Sure can't do it with that little flow meter! I guess pulling plugs is about the only way. But then what does one do? Adjust the flow to get it better at higher RPMs? That would then throw it off at idle, and then we get back to not having a cylinder fire at idle.

I would recheck it at the highest flow your sych meter will read - whatever RPM that is.

I am wondering if perhaps it is too rich. When cold that extra fuel is good, but when hot it is not. But we are already down to a 55 idle jet from 60 so . . . . . May be a larger air jet?

Despite the rising frustration level, still plan to pop the tops off the carbs check for sediment and recheck the float levels.

I would not be messing with air jets yet - you need to get the idle circuit under control - that is where you will do most of your driving. Being on the too rich side of the equation can produce some of the results you are seeing. Do you have a exhaust gas analyzer available? If not, I have one I can send you or I can show you one that costs less than about $150 that I used to determine I was way too rich on one weber installation.

Oh and one other issue. For fifteen minutes after shut down one of the forward carbs spills gas into the throat of the carb. You can see the puddle of gas just setting on the throttle plate.

Have you got the proper fuel pressure to these carbs - 2-3psi?

I am just about ready to buy an Edelbrock intake manifold and a Holley carb. But Ryan does not want to give up yet . . .

Don't do it - yet! Honestly, and please don't take this personally (I am trying to help)but fomr what I am reading, I think it could be your process. I am just trying to help, but, having gone through this during my learning curve with these carbs - and then coming out the other end - the process is critical (I think). See my post above.

Regards,
Mike

 

[Mike Christian]

Re: Weber Carb Issues

Idle stop screws


3. Keep all four idle stop screws, adjust for proper flow, and then adjust the linkage to match those settings.

The downside of using more than one stop screw is one may not precisely match the lnkage to the stop screw setting, it would seem to me.

Plus if more than one idle stop screw is kept in play, how would one finalize the idle speed adjustment? Adjust idle with more than one screw than recheck with the flow meter?

You can set your idle screw position on all carbs with the linkage disconnected (that is part of the process). Then when your carbs are flow matched and you attach the linkage, you can keep the idle screw in play or remove some from play. If your linkage is a good one, then it shouldn't matter really.

[Throttle Springs

All four carbs have throttle return springs. I have seen some sources recommend removing the springs from the two dependent carbs so only two return springs are used.

I have all four in place. Perhaps the extra tension contributes to unreliable alignment?

You want all butterflys to track the same as determined by airflow throught the carbs. If the linkage design is good, you should not have to worry about "unreliable alignment". This is IMO not something to worry about yet - you still need to get the carbs working right with linkage disconnected. That is, unless disconnecting return springs is recommended by your linkage manufacturer.

Regards,
Mike

 

[Jac Mac]

Havent had time to read thru all this but two thoughts : Valve guides, particularly exhaust hanging up/sticking from partial seizure - due mainly to seals actually working too good and a lack of oil up top, and over on Club Cobra there have been others having problems that have been tracked down to poorly machined jets, threads etc--- one in particular being the pump jet ball seat which allowed fuel to pass full time. Carbs, not only Webers, seem to have suffered from poor QC over the last decade or two, simply cannot take anything for granted these days.

A leakdown test ASAP after the misfire occurs might find it, & the carbs need a good set of eyes & magnifying glass for the latter.

 

[Chuck]

Took the day off from the GT and restored a piece of antique furnture for my daughter. Sometimes working with a table saw, glue and stain can be good therapy for Weber frustration syndrome.

Spider Mike: Thanks for the detailed post. I am printing it out and pasting it on the garage wall as a reminder and for reference. I appreciate the time you spent responding to my issues.

Randy: The fuel pressure is right at 2.5 lbs. Will check the floats when we pop the tops off the carbs (Waiting for a set replacement gaskets to come just in case I damage one when doing this little project).

Jac Mac: Good points. Guess we just can't assume things are put together right anymore.

Will jump back into the carb this week. Got 250 miles on the GT already and everything else is so good!

 

[Dave]

Oh and one other issue. For fifteen minutes after shut down one of the forward carbs spills gas into the throat of the carb. You can see the puddle of gas just setting on the throttle plate.

My 44 idf set up does this aswell, I am having the exact same problems.
Evry problem you have I have aswell.

Brand new 302 IDF set from Webers.com. 2 carbs work perfect, 2 are dogs. I am also finding that some of the carbs respond really well to mixture change others take 3 or so turns to get the cylinder firing.

I 've cleaned, balanced, jetted and so on with no luck.

I'm not trying to steal your thread just letting you know that someone else in the world is having the exact same troubles and it may not be your motor but an issue with the carbs.

 

[Chuck]

Dave:

"Misery loves company."

Seriously, keep us posted on what you do and the results. This issue will get resolved. . . . . .

 

[Mike Christian]

2 carbs work perfect, 2 are dogs. I am also finding that some of the carbs respond really well to mixture change others take 3 or so turns to get the cylinder firing.

And your mixture screws have the exact same profile?

And you have checked that the holes in the idle jets are the exact same size?

Mike

 

[Chuck]

<B style="mso-bidi-font-weight: normal"><U><SPAN style="FONT-SIZE: 14pt"><FONT face="Times New Roman"><FONT size=4>Weber Carburators Revisited, Part I<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com

<o></o>
We decided to go back to the basics and start over. First, the linkage.
<o></o>
The bolt that holds the bellcrank was not tight. Upon tightening it the support post, it no longer moved. So we removed it. Turns out it had been installed upside down, since the bearing sets below the surface of the bell crank on one side to clear the mounting post. Reinstalled it and tightened it down. Now it turned easily. This likely added a bit of slack to the system we had not previously recognized, but is now corrected.
<o></o>
Next attention was turned to the two connecting arms. The ends had been cut off rather sloppily at an angle. A quick measurement confirmed that one was 3/16 inch longer. This could affect the synchronization when the carbs were progressed towards a more open throttle position. So some time with a file evened up the ends and made the two equal in length.
<o></o>
I expected the linkage to have been properly assembled on this dyno run crate engine. Big mistake. Guess one should never assume anything.
<o></o>
Each carb has a separate throttle return spring. We removed the springs on the two dependent carbs (the ones not directly connected to the bellcrank). This reduced the resistance in the system and took some potential tension off the throttle shafts.
<o></o>
Next the idle stop screws on each carb were set to just barely touch when the throttle plate was fully closed. Only one idle stop screw will be used for idle adjustment, but the remaining three will provide a reference point for fully closed.
<o></o>
Finally we added a separate return spring that connects to the bell crank. The amount of spring tension can be easily adjusted with this spring.
<o></o>
Tomorrow we will pull the tops off the carbs, check the float level and make sure there is no dirt inside.

 

[Mike Christian]

In my experience, starting from scratch would mean disconnecting the carbs and dialing them in without the linkage attached. Then you attach the linkage and work out those bugs...my two cents worth.

From the picture you attached - the overhead shot of the setup, the two little hexbars coming off the center are not parallel...therefore, I would expect that they will open the throttles at different rates. Is this a "before modification" picture or an "after modification" picture?

Kind regards,
Mike

 

[Chuck]

Mike:

You have a sharp eye. I had also noticed that the connecting arms were not exactly aligned the same. But not quite sure how to make them parrallel. The lower arm (in the picture) can't be moved any closer to the carb or it will hit the carb linkage. A washer would push the top arm in the wrong direction. Any suggestions?

The idea of bending the linkage arms on the carbs does not appeal to me.

Your pont on synching the carbs with the linkage disconnected is noted. My plan was to start up the engine and let it warm up, then disconnect the linkage. It needs a bit more than low idle to get it running and with the linkage fully disconnected thought it might be a bit of a challenge to get the engine warmed up.

Since you would remove the linkage, I suspect you would adjust each of the four idle stop screws and then leave them in place, then connect the linkage without disturbing the stop screw settings. I note that Pat Braden, in his Weber book, uses only one idle screw and then adjusts the linkage to synch the other three. Your approach would seem to give a more definite idle stop point, since the idle stop screws would presumably be a bit more reliable than the linkage. Is that your thought?

From what I have been reading, my impression is that the throtle plate should be essentially closed in the idle position, opened only the bare minimum necessary to get the four carbs synched. I suspect one of my problems may have been that the throttle plates were too far open.

I really apprecate your comments.

Chuck

 

[Dean Lampe]

Chuck, Your arms are a lot closer to parallel than mine and mine runs great. I wasn't able to get mine perfectly synched at idle resting on the stops AND off idle with tight linkage so I opted to set my synch at about 1500 with part throttle, essentially taking the throttle stop out of the picture. These cars are often a series of compromises. It idles fine but it screams as it comes through the rpm range.

 

[Ian Clark]

Hi Chuck,

Lot's of great advice on this thread, wow! I agree with everyones input, just goes to show how many ways to skin a cat (maybe that's politically incorrect to say these days, sorry).

Politics aside, it's evident making sure everything else outside the induction system is working properly has to done.

The carbs have to be individualy inspected and verified to be working properly, no damaged mixture screws, no mismatched jets or emulusion tubes, proper float level, no worn or dried up throttle shafts, proper throttle plate alignment in bore, clean and properly assembled.

Then it's setup and tuning. I'm glad you went through your linkages, it seems these parts are simply bolted together for ease of shipping. Nothing is really done regarding setup.

I'd be tempted to leave the throttle springs in each carb, it shouldn't matter unless the spring pressure is bending a connecting tab between the carb pairs on one bank. If that's the case the tabs are junk. Haven't seen that one yet.

Mike's got the right idea having all the linkages off when doing the initial settings. Since you have a central bellcrank linkage you have two lead carbs, one per bank. The idle screw has to be used on the lead carb(s). In a single cross bar setup where the throttle cable pulls on one carb only and the cross linkage pulls the other bank, you have one lead carb. In theory you could get away with one idle screw. Not your setup, just an explanation of one vs two idle stop/speed screws.

It gets real tricky with making sure the take up of linkage free play is equal and the banks of pairs open the same. That's the key to off idle tranistion and low speed around town cruising.

The two cross linkages do not have to be equal, when the final settings are found you may discover unequal lengths. This would indicate asymetry in the manifold regarding location of the carb banks or center pivot. This is not a problem as it can be dialed out.

How long or short you run the cross linkages will affect the rate of pull on the carbs or "throttle tip in". Longer gives slower tip in and ease easier to adjust, just make sure you leave enough threads in the shafts and don't cause binding at idle.

If you're running a hydraulic grind cam, maximum safe timing, 2.5 > 3.0 psi fuel pressure, no vacum leaks and have everything clean and syncronized it will run beautifully. Oh yeah, about fuel pressure, the engine must be running to check fuel pressure, regulators aren't accurate without flow.

Cheers