Carb issues take two, Idle still dropping off Dual IDF 40s Options

[VaccaRabite]

If you remember from my last thread, I have started having an issue where my idle was dropping from 1100 to ~500 and the engine would sputter. I thought it was due to clogged idle jets.

Well, Friday I cleaned the dickens out of my idle circuits and set idle back to 1100. Yesterday (saturday) I drove the 914 70 miles to Plaskets' summer BBQ. The car did great until I got to within a few miles of Plaskets, with the idle falling off again. ScottyB and I tinkered with it for a while - checking timing and trying to figure out what the hell was going on.

What we found was that the drivers side bank of carbs was dropping out, possibly due to the idle stop backing off. But the carbs were just being wonky. We ended up not really fixing anything. I set idle back to 1100 and headed for home. the 70 mile trip was more or less uneventful until I for a mile or so away from my house. Stopped at a light and almost home, I could feel a cylinder drop off. The idle dropped down to about 1000 rpm and the idle became just a little lumpy. When I got home, I was back to idling on 2 cylinders at 500rpm and the car was sputtering in my driveway while I waited for the garage door to open. I had to keep blipping the throttle to keep it alive.

The thing is, as son as you give the car gas, all four cylinders fire up and the car is a blast to drive. Its just back down to idle where I have issues.

I am at the point where I am going to unhook the linkage and start from scratch to rebalance everything, and hope that fixes it.

If anyone has other ideas as to what is going on I'd love to hear them!

Zach

[brant]

I sometimes have the same issue when hot. I can't wait until you solve this for me......

I've balanced the carbs with linkage attatched.
what is the full rebalance procedural steps with the linkage unattatched (that you are going to do)
?

tia
brant

[neyen14]

I had this problem... I have the CB performance linkage... don't know if you do or not. What was happening for me was that the 45 degree bar that actually connects the hex bar to the linkage at the carb was loose. The little screw that holds it to the hex bar needed to be tightened... and that was all.

[VaccaRabite]

I sometimes have the same issue when hot. I can't wait until you solve this for me......
I've balanced the carbs with linkage attatched.
what is the full rebalance procedural steps with the linkage unattatched (that you are going to do)
?

(IMG:style_emoticons/default/laugh.gif)

When I do a full balance, I start with one end of the linkage unhooked and set my carbs idle only with the idle stops. Fully wamred up, etc, I can set my idle where I need it to be to have all the carbs drawing the same. Then I can fiddle with the mix screws to get them perfect. Then fiddle with the air correction screws (if needed) to get all four barrels exactly the same.

When all that is perfect, ten I hook up the linkage. the idea will be to have the arms set to not be pushing against the idle stops, but be right on them. Then you try to adjust so that idle does not change but the carbs are still balanced at WOT.

So, I am starting over from scratch. Hopefully this works.

Everyhting was running great earlier this summer before I went up from 55 to 60 idle jets. (IMG:style_emoticons/default/dry.gif) Maybe I'll set them back down to 55s again when I reset.

Zach

[brant]

are their idle stops on both banks?
I can't remember mine without looking... but know the idle stop is adjustable on one side. Need to look at the 2nd side this evening when I go attempt this.

brant

[VaccaRabite]

are their idle stops on both banks?
I can't remember mine without looking... but know the idle stop is adjustable on one side. Need to look at the 2nd side this evening when I go attempt this.

brant

Yes, idle stops are on both banks of carbs.
I have seen some folks say that you should only have the idle bank on one set of carbs active, but on my hex bar linkage there is just enough slop in it to throw off the idle on the other side. 1/16 of an inch is the difference between success and failure. Maybe I just need to move to a different style of linkage, but I know others have gotten the dumb hex bars to work for them.

Instead of the spring tensioners on the idle screws, I am thinking of using lock nuts once I have idle set. That way I can eliminate the idle screw backing off as part of my issue.

Zach

[ME733]

............Well it is obvious you guys have a modified/performance camshaft....and you EXPECT the engine to have "stock" idle range abilities....IT AINT GONNA HAPPEN.........Solution: reset you idle to 1500 rpm,s.,it will idle fine at that idle speed....THEN start lowering your IDLE rpm,s in 100 rpm increments,....until you get the engine dropping cylinders syndrome you now have.....YOU are never going to have a stock idle.

[brant]

............Well it is obvious you guys have a modified/performance camshaft....and you EXPECT the engine to have "stock" idle range abilities....IT AINT GONNA HAPPEN.........Solution: reset you idle to 1500 rpm,s.,it will idle fine at that idle speed....THEN start lowering your IDLE rpm,s in 100 rpm increments,....until you get the engine dropping cylinders syndrome you now have.....YOU are never going to have a stock idle.

Nothing obvious here.
no time to play arm chair quarter back
cam profiles don't "change" between a hot motor and cold motor, especially at random....

I think the original poster is able to keep a solid idle most of the time and has recently experienced an intermittent change. ie: something is not right, or not as it normally is.

It's easy to see what is obvious here

[VaccaRabite]

Indeed. My car idled like a rock at 1100 rpm all summer long. Earlier this month I bumped my idle jets up to 60 from 55, and reset the carbs for the new jets. Thats when this weirdness started happening.

This is not cam related. (IMG:style_emoticons/default/rolleyes.gif) This is getting my induction correct.

Zach

[Root_Werks]

Zach,

I bumped my 50's to 55's a while back which really helped to smooth things out. After a handful of miles, kinda the same issue, kept dropping a cyl, at times two!

Fiddled with adjustements seemingly to no avail.

Pulled a spark plug for the cyl not responding, fuel fouled. Doh.

Popped in just one used plug I had sitting around, ran perfect. Zipped down to the parts store and grabbed 4 new plugs.

Point is, don't forget to check the simple stuff which I seem to do often. (IMG:style_emoticons/default/rolleyes.gif)

[VaccaRabite]

You know, we did not check plugs yesterday. I like this concept.
When I went from 55 to 60, I might have gone from a tad lean to a tad rich idle. Driving around town I am mostly just off idle or coasting. Maybe the plugs are just starting to foul. maybe the solution is to buy a set of 57 idle jets from Aircooled.net and see what happens?

Zach

[karnak]

hi Guys,

i was poking around and decided to join in. (first post) (IMG:style_emoticons/default/piratenanner.gif) i wanted to add that i had a similar issue with my carbs. a random issue that stayed with me for waaay too long. i ended up doing all the usual stuff like wires and plugs but the problem was fuel. i put in a 10 micron fuel filter with cleanable filters and the unpredictability went away. the next thing i addressed was the fuel mixture. i purchased a "Gunson" color tune spark plug and tuned the mixture by color (of the burn) . it was good to do since i was guessing at the mixture settings... good luck!

(IMG:style_emoticons/default/driving.gif)

Gary

[jmill]

Even with the idle stop screw backing out you wouldn't drop a cylinder. You'd just close the butterfly all the way giving you a really low idle. Dropping a cylinder means you fouled a plug or have a plugged idle jet.

Getting a better filter and running one at each carb and one at the tank should catch the gunk. Your 1100 idle is a bit high. Even with a healthy cam you should be able to get it lower. Dual carbs smooth out lumpy cams.

Instead of investing in smaller jets, turn in the idle mixture screws a bit. It wont affect the volume through the progression ports but you'll have less flowing out of the idle mixture screw port. It'll lean up your idle a bit.

[rhcb914]

Not sure what type of fuel filter you are using but I agree with jmill and karnak that you should make sure you have excellent fuel filtration. I run dual 40's and used to use the clear plastic carb filters but they would let all sorts of gunk by. I finally re-worked my fuel lines over the winter and used a FI filter and have not had any issues this year.

I was however intermitently dropping a cylinder on idle but that was because the idle mixture screw was turned in too much. As soon as I would blip the throttle the cylinder would come back for a few seconds then die out. Backed it out 1/2 turn and it's fine.

Good luck. Interested to see what the outcome is.

[Dr Evil]

(IMG:style_emoticons/default/popcorn[1].gif) I got nothing....

[type2man]

I would first start off with a new set of plugs. I recently switch from Bosch to NGK's and they work great.

I would check the idle stop screws to make sure they dont turn freely and they have the springs on them.


You could have an intake leak at the head when the engine warms.

[VaccaRabite]

My immediate plan of action is this:
pull and inspect and probably clean my spark plugs. They are brand new this spring so I doubt I need to replace them, but they might need cleaning.

Change my idle jets back down to 55. Retune the carbs for the smaller idle jets. Drive it and see where I stand.

I was not having this problem with the 55s, and it will only be an afternoon to bring it back to a known good state. If the problem persists I know I need to fix something else. But I think I am just too rich at idle right now and am fouling plugs.

Zach

[ME733]

............Well it is obvious you guys have a modified/performance camshaft....and you EXPECT the engine to have "stock" idle range abilities....IT AINT GONNA HAPPEN.........Solution: reset you idle to 1500 rpm,s.,it will idle fine at that idle speed....THEN start lowering your IDLE rpm,s in 100 rpm increments,....until you get the engine dropping cylinders syndrome you now have.....YOU are never going to have a stock idle.

Nothing obvious here.
no time to play arm chair quarter back
cam profiles don't "change" between a hot motor and cold motor, especially at random....

I think the original poster is able to keep a solid idle most of the time and has recently experienced an intermittent change. ie: something is not right, or not as it normally is.

It's easy to see what is obvious here

Yes it is obvious, you have , apparently, such little experience, with modified engines, that you do not even understand what it is you have stated in your post.(which is nonsense ).....The engine in question has a modified cam..as he stated in a previous post....the engine in question ALREADY has an idle well ABOVE stock idle.(and dropping cylinders).....SO.. if you don't want to pay attention to some one with experience, making comments to HELP resolve the problem fine. There are other steps involved in getting this engine to run properly, at lower rpm,s and Idle properly.crisp and clean...with out having to change spark plugs frenquently due to their failure from a too cold/rich mixture, and eventually oil fouling.

[brant]

Murry,

your posts are often negative and belittling.
very negative.

Even if you have experience and knowledge that is useful, its hard to listen in the way you present. I find very little positive or helpful when you post.

perhaps go back and hang out on the originality forum?

[Cevan]

You know, we did not check plugs yesterday. I like this concept.
When I went from 55 to 60, I might have gone from a tad lean to a tad rich idle. Driving around town I am mostly just off idle or coasting. Maybe the plugs are just starting to foul. maybe the solution is to buy a set of 57 idle jets from Aircooled.net and see what happens?

Zach

I think we have pretty similar engines. I'm running 57s and they seem to work fine. My car will idle fine at 500 rpms if I want it to.