If an intake valve was adjusted too tight, could it cause symptoms similar to a vacuum leak? What are the symptoms associated with too tight intake valves?

When I start my car, the rpms go to about 2500 then drop after about 10 seconds. If I rev the engine, the rpms do not drop for about 10 seconds. When I am driving the car, if I put in the clutch, the rpms often rise.

I did have a cracked intake manifold (running dual idfs). I replaced the cracked manifold and readjusted the carb links and the engine still has the same issues. I have only driven the car twice over the past year. I did some work on the valve train a few weeks prior to the rev issue. I have to check the valve lash anyways, I just thought I would get peoples opinions.

-I am 99.99% positive that it is not a carb linkage issue.

99% of carb problems are electrical. In you case I think you are a 1% er. I would double check the lash but you posted your car was sitting a long time. You may have an internal leak in one of the carbs allowing excess fuel to dribble for a period of time holding the idle up until the excess fuel is burned off. I'm no expert but that's what I got from what you posted.

It'll be real quite and then it will probably burn the seat. If it's too tight it will loose compression on that cylinder and will backfire back through the intake.

I'm 99% sure it IS a carb linkage issue, assuming the timing is right and there are no vacuum leaks. In no way is it a result of a tight valve.

The Cap'n

I am running chromoly pushrods. I was a little nervous about setting the lash at 0. This is what caused me to think that there may be some connection.

I have checked over and over with carb cleaner, brake cleaner, starter fluid, wd40 and I cannot find a vacuum leak.

I am using a bell crank linkage. I synced the carbs with the links detached. I then connected the links and made sure that the lever was resting properly on the idle screw on the carbs. When I start the car, I get a rpm surge then it comes down. If I rev the engine, it takes a while to return. I visually confirmed that the lever was resting on the idle screw when I was having the rev issue. I have even started the car with the linkage disconnected and the rpms still shoot up then drop. I am out of ideas on how to check the linkage.

My engine was rebuild about 2 years ago. I have been slowly working on a bunch of things on my car which is why it has been sitting. Pretty much everything is brand new or freshly rebuilt.

I have a bosch 050 dizzy. I have it set at 32degrees at 3200rpms. Is this correct?

Thanks again!!

If the air cleaners are off use a piece of cardboard across the top of the carbs on one side then the other and see if you can determine which side or if it is both sides causing the high idle. You might also try some plastic bag material with a rubberband around it to hold it on. Don't let it get hot and melt though. If the squirters are easily unhooked you might try opening the butterflys while the motor is off and see if any fuel is leaking down inside the carb. If you just open the butterfly to look, it will squirt on each stroke it is opened and you won't be able to tell if it is leaking. Sometimes if you shut the motor off and fuel is leaking down inside the carb it will smoke some out the top of the carb just setting if the motor is hot.

BE CAREFUL though a backfire will remove your eyebrows and lashes at the least.

.................DO NOT USE PLASTIC BAG MATERIAL OVER THE CARBURATOR WITH A RUBBER BAND....It,s NOT Strong/ridig enough to prevent it from being sucked into the carburator/manafold....cardboard OK.....And check the strength of the EXTRA CENTER MOUNTED return spring on your carb linkage (got one right)...sometimes the O.E.M. wound springs,on the side of the carburator get tired/old and loose their tension. Most noticable at idle or right after you come off the throttle....as engine "hunts for the idle setting, rpm,s"....also check that the emulsion jet tube.holding the air correction jets and main jets is tight in the carburator.also Float level could be just a little too high.

My carbs seem to snap back to idle pretty easily. It wouldn't hurt for me to get new return springs. Does anybody know where to find the circular shaft return springs. I quickly searched and couldn't find any.

I am concerned about my timing. For a bosch 050, does 32 degrees at 3300 rpms sound reasonable?

Also, could somebody give me more details about the covering up one side carbs to figure out which side is a problem. What should I be looking for when I cover the bad side?

I would look for the clutch cable tube being broken away from the chassis or the throttle cable wrapped around the clutch cable.Sounds like a fuel delivery problem to me.

[quote name='ME733' date='Jun 26 2010, 07:51 AM' post='1335353']
[quote name='charliew' post='1335279' date='Jun 26 2010, 12:29 AM']
If the air cleaners are off use a piece of cardboard across the top of the carbs on one side then the other and see if you can determine which side or if it is both sides causing the high idle. You might also try some plastic bag material with a rubberband around it to hold it on. Don't let it get hot and melt though. If the squirters are easily unhooked you might try opening the butterflys while the motor is off and see if any fuel is leaking down inside the carb. If you just open the butterfly to look, it will squirt on each stroke it is opened and you won't be able to tell if it is leaking. Sometimes if you shut the motor off and fuel is leaking down inside the carb it will smoke some out the top of the carb just setting if the motor is hot.

BE CAREFUL though a backfire will remove your eyebrows and lashes at the least.
[/quote]
.................DO NOT USE PLASTIC BAG MATERIAL OVER THE CARBURATOR WITH A RUBBER BAND....It,s NOT Strong/ridig enough to prevent it from being sucked into the carburator/manafold....cardboard OK.....And check the strength of the EXTRA CENTER MOUNTED return spring on your carb linkage (got one right)...sometimes the O.E.M. wound springs,on the side of the carburator get tired/old and loose their tension. Most noticable at idle or right after you come off the throttle....as engine "hunts for the idle setting, rpm,s"....also check that the emulsion jet tube.holding the air correction jets and main jets is tight in the carburator.also Float level could be just a little too high.
[/quot ..............AND...with the bell-crank linkage...Remember the engine will expand.,as it gets hot... As it does so the distance between the carburator arms increases.IF you set the idle adjustments, idle screw,on the carb linkage arm,when the ENGINE IS COLD there will be a SLIGHT TENSION (preload) which can cause a higher idle when the engine is HOT....set the idle adjustments, rod lengths,stop clearancess, with the engine HOT. ...............The carb. wound springs (on carb body)can never overcome the tension (from the increased expansion distance) (a preload) from the bellcrank arms (accelator linkage) to carb arms, if idle...stops... are set... ON A COLD ENGINE. ......Again , Idle and linkage distances must be set with the engine HOT with the bellcrank linkage set up. ...............And sometimes a distributor with "sticky"return springs (sometimes caused by rust inside the distributor) will not want to pull back to the idle advance setting immediately..A drop of oil inside the shaft, or on the springs might help. check to ensure the rotor snaps back...Completely....each time,when rotated.(a worn rotor-loose on the shaft) can also be a culpret/problem.

If it was a pushrod issue then it would be tight when the engine was cold, normal when the engine was hot. Chromoly does not grow nearly as much as aluminum, so 0 cold grows to normal lash when hot. You can pull spark plug wires off to find cylinders that aren't working right, but it won't tell you why.

Did you use a synch to test your carbs? It is the best way to eliminate that as a problem.

I synced the carbs when the engine was cold. Later tonight, I will resync everything when the engine is hot and see if that works. It is ver.y possible that is my problem.

I used a snail to sync the carbs. My problem is that I am sucking in almost too much air for the snail. The reading is very close to the top making it hard to read accurately. I do have a unisyn somewhere but I have not been very good with those.

Thank you to everybody for the help. I will post an update after my resync tonight.

There is also a "bench" setting for the carbs. Do you have the Webber tech manual? Something about screwing the idle screws all the way in, backing them off a few turns, using the sync to fine tune them.

I'm sure somebody here will complete my vague information...

Carbs have to be synchronized at normal operating temperature. The slow to return to idle problem could be caused by the mixture being way too rich. 32 degrees is higher than I'd go with an air cooled engine. I generally use 28 degrees, 30 tops, to cover myself against potential engine damage on a street engine.

The Cap'n

You will do far more damage to your valve job with to much lash than to tight when dealing with chromo pushrods. If to tight the engine will be hard to start, but once running the lash will increase. If to loose you will hammer the valve seats. This condition is aggravated if your valve springs are weak and you like to twist that baby up (lots of revs). That REALLY beats the snot out of your valve seats. I have seen this combo beat the intake seats right out of the head.

There is a bench set for initial startup. It involves using a feeler gauge on the butterflies with the carbs off. You set the idle stop screw to have the butterflies open .004. Check both to make sure you don't have a tweaked shaft. Set the bypasses at 1/2 turn out (I keep them closed). Set the mixture screws at 3 turns out.

Start the car and adjust flow (idle stop) on the 2 barrels closest to the linkage. When flows are equal adjust rods and connect linkage. Set mixture for best mix (mixture screws). Set idle speed (idle stop). Mirror turns on idle stop screws on each side. 1/4 turn at a time until your idle speed is correct. Equalize each barrel flow (air bypasses).

With the chromo rods you should be safe to run zero lash. I am, with no problems or tight valves after a few thousand miles and an adjustment. I agree with everyone else that your issue is carb balance, not valves.

I went out, confirmed that the carbs were synced. I played around some more then decided to start the engine with the barb links disconnected. The engine didn't rev abnormally. Here is a link to the video-

http://www.youtube.com/watch?v=uAvoM4DpyyM

So my question now is general. After listening to the video- does anybody hear or see any thing in the video that I need to address. Someone may notice that my I have the distributor backwards. When the PO rebuilt the dizzy, he put the little offset tab thing that connected to the drive pinion backwards. I got used to it this way so when I rebuilt it, it was built the way the PO did.

I have a super rich mixture. I am not sure why however this is an issue for another thread.

with the droplinks/threaded rods not attached and you have a nice stable idle, i'm 99% sure you have a linkage issue.

no way should your engine zoom up to 2500 rpm upon start up nor should it not go to a 900rpm when you take you foot off of the pedal. i think you might have a binding issue. whether in the cable or the linkage.

trying to achive balanced carbs with the idle speed adjustment screws is a WASTE OF TIME AND FUEL. if the linkage is wrong, the carbs will fall out of balance as soon as the butterflies open and screws are off the stops.

when you are syncronizing the carbs with the unisyn tool, just turn the idle up enough to stop the pulsing of the needle. you can raise the lidle and check for balance with the linkage attached by simply turning up one (1) idle speed adjusment screw. the other carb will (should) follow. do this and see how the carbs match up with the needle not fluctuating. if you look at the base of the unisyn the is a hole in the bottom and one in the rubber sealing ring. lining up the 2 holes will make the unisyn less sensitive to vaccum pulses.

I have found that the arms of some hex bar set-ups have had a variance in their ratios. With the one on my race car I had to drill a new hole in one to even the ratios. If I set both carbs so they would see full throttle one wouldn't shut all the way. If I set them both where they would shut all the way one wouldn't open to full throttle! Very frustrating!
It's one of the reasons I'm looking forward to Jake getting the Acculink linkage sorted.

I'm sure glad this was a real thread....I was afraid that "tight intake valve" was code for something unspeakable....what a relief.....

My 2056 had the same thing, the PO installed the dizzy 180 deg. off.

Never ran right until i put it all back to where it should be ...
Andy