2F perfect idle to crap idle in one second. (1 Viewer)

[island45]

'79 2f , '77 aisan carb, compression 160-170 vacuum 19. I started out last year with a Chinacarb. It ran very well in all respects, until one day it didn't. Instead of investigating I had a '77 carb I found in my attic and had had intended to send to one of the guys here to rebuild. I decided to bolt it on as is and it started and ran flawlessly. Great power on the hills and a silky smooth idle, literally like a watch. This perfection lasted almost a month til about four days ago when I was loading some tools in the back to go to a jobsite. The perfect idle suddenly went really rough and then engine died. It restarted fine and would idle, but not well with the choke knob out about 3/8" . Carb cleaner at the carb base showed some increase in rpms. Idle mixture screw did nothing, even seated. I surfaced the manifolds last year and used a remflex gasket. Tank is new 17 gal aluminum fuel cell with inline filter. Fuel pump new oem. Checked all vacuum hoses which are Mcmaster carr silicone. Fuel level in sight glass right on 1/2. Pulled pcv and capped hose, no improvement.
I pulled the carb and checked the intake floor under carb for cracks with my 2.75 reading glasses on and a LED flashlight. Nothing found. I see daylight through idle mixture passage with needle out, blew some air through just because. I used some 1/16" soft gasket material and made new gaskets above and below the insulator after a careful cleaning. I had one sketchy carb stud which I fixed. Ran exactly the same. I ran it to town and back, 24 miles, still same.
My take on this is there may have been crud in the float bowl that got picked up and sucked into a passage (or jet?) controlling idle circuit. Maybe the idle solenoid, but my take is it wouldn't run at all if it was faulty. Would love to hear about where to blow air or run a piece of wire or monofilament through or somehow to chase this problem down. With the perfection of idle and strong running 5 days ago I hate to send this out for a rebuild, specially since we finally have some summer weather and rig would be down for a long period. Any ideas would be very much appreciated.

 

[fyton2v]

Rebuilding it yourself is an option. It’s not hard, and it’s a lot faster. Take a bunch of pics, use the manual, watch Pin_Head’s YouTube videos, get organized, do it.

The accelerator pump that comes with rebuild kits is mostly junk. You could spring for one that uses a leather seal from City Racer’s store. It solved a hesitation issue that plagued my 2F after I did my own rebuild.

 

[island45]

Thanks fyton, I am half way through pinhead's video series. I started last night and yes, seemed straightforward. I have rebuilt maybe ten carbs from '30s-'50s trucks correctly over the years, but was thinking with this carb's initial proven performance and it's remaining good drivability as is, that there is just something amiss with the idle circuit and I would hate to disturb the other 90% of the carb. Pulling the choke out at stop signs is getting old... Back to the pinhead series!

 

[peesalot]

Check fuel bowl, filter & tank for crap, maybe rig up a gas can as a temp tank with new filter and see.
Check for vacuum leaks ( Booster)
Check spark plugs.

 

[island45]

Ok, thanks. Booster line is removed and capped, still same. Should I pull the top off carb while it's on the vehicle to check bowl? And the spark plugs, not yet, but there is a small part of me that remembers an old addage... '90% of all carbureuter problems are ignition'. Was there a particular reason you suggested looking at the plugs? I'm game for anything at this point. The sudden-ness of all this bad idle stuff doesn't seem to lead to problems like worn throttle shaft etc. Can an idle/fuel solenoid get weird and cause idle issues? Maybe I'll swap it out for a used one in my kit and check back.

 

[peesalot]

The fact you say you have checked idle circuit and it was clean, I had a intermittent issue similar and it was from water/debris in tank getting into system and causing random, spotty running issues so check bowl, filter, tank. From exp. sudden symptoms like this has been spark plugs & or coil. Vaccuum leaks can be sudden and are easy to diagnos so why not have a look.

 

[peesalot]

Yes, the idle fuel solenoid needs to function correctly, could be simple as a fuse for that.

 

[77mustard40]

Carb cleaner at the carb base showed some increase in rpms.

Man this sure sounds like a vacuum leak, have you looked at your vacuum reading after all the work you’ve done? A rebuilt 77 carb should be a good match for your 2F.

 

[45Dougal]

"Carb cleaner at the carb base showed some increase in rpms."
How do you explain this?

Sounds like a gasket or shaft leak, unless it was displacing some water in the ignition briefly

 

[mattressking]

I usually repeat these tests once a week with folks, I’d like to make a sticky or a video because it gets really old repeating it.

1. Measure vacuum at idle when hot. Must be 18inHg or greater and choke completely open. Anything less will degrade carb performance and cause hesitations.
2. Timing must be 7* to start, anything greater could be masking a vacuum leak.
3. If choking helps that means there’s too much air (usually).
4. Verify the ICS clicks reliably and power is switched +12v.
5. China carb is a question - have you verified float level is visibly in the middle while running?

Answer those questions honestly and completely then we can diagnose further. Don’t waste your time checking anything else until those basic facts are answered as of now when the issue is apparent.

 

[island45]

Thank you Mr. King! Sounds like a common sense approach. Unfortunately I spent most of my day yesterday fixing the hydraulic tilt on my son's boston whaler and couldn't jump onto what I really wanted to do. Today after work I will go through this checklist in a methodical manner. Carb is a '77 aisin, the china carb was relegated to paper weight status last month... Does the BB mark 7 degrees? One more question before my test. Right now the dist vacuum line is at one of the two poirts facing dist at base of carb. Is this a good port? I dont feel vacuum there. And do I unhook the dist vac line to do my 7* test?

 

[island45]

"Carb cleaner at the carb base showed some increase in rpms."
How do you explain this?

Sounds like a gasket or shaft leak, unless it was displacing some water in the ignition briefly

I made new gaskets from a fairly thick pliable material and applied to both sides of very clean insulator. Applied grease to shafts with a small paint brush, no change. I will know more after work today. Running a woodworking shop here behind the house just could mean an early quitting time. The suspense is killing me.....

 

[45Dougal]

I made new gaskets from a fairly thick pliable material and applied to both sides of very clean insulator. Applied grease to shafts with a small paint brush, no change. I will know more after work today. Running a woodworking shop here behind the house just could mean an early quitting time. The suspense is killing me.....

I hope you're not sitting back there whittling about it

Maybe see if the spray still has an effect after the gasket fix.

Good luck

 

[mattressking]

Thank you Mr. King! Sounds like a common sense approach. Unfortunately I spent most of my day yesterday fixing the hydraulic tilt on my son's boston whaler and couldn't jump onto what I really wanted to do. Today after work I will go through this checklist in a methodical manner. Carb is a '77 aisin, the china carb was relegated to paper weight status last month... Does the BB mark 7 degrees? One more question before my test. Right now the dist vacuum line is at one of the two poirts facing dist at base of carb. Is this a good port? I dont feel vacuum there. And do I unhook the dist vac line to do my 7* test?

Yes, BB marks 7*. When setting time ensure all accessories are off and vacuum lines to distributor are removed and capped. You shouldn’t feel vacuum at idle as it is ported vacuum. The moment the butterfly begins to open you should begin feeling vacuum progressively.

 

[island45]

Had a meeting about an upcoming job and it ran long.... I have the BB centered in the window. It was just a bit advanced. Funny, all instructions I can find say to have choke open and engine at temp and idling to check vacuum and timing. With choke open, engine dies.... next the carb cleaner. I'll be back.

 

[island45]

Yes, BB marks 7*. When setting time ensure all accessories are off and vacuum lines to distributor are removed and capped. You shouldn’t feel vacuum at idle as it is ported vacuum. The moment the butterfly begins to open you should begin feeling vacuum progressively.

Thanks, we were typing at same time.

 

[65swb45]

With choke open, engine dies....

That and the lack of change from adjusting the idle mixture screw SCREAM idle circuit.

So then the question becomes, victim or culprit? Insufficient vacuum =victim. Sufficient vacuum =culprit.

 

[island45]

Inconclusive so far. I had only a very small amount of carb spray and town is 24 mile round trip. I used mapp gas and carefully went around all suspect areas with the exception of under the insulator shield. No change, but does mapp gass work for this? I have heard of people using propane. I sheepishly sprayed some either but it makes a big cloud and doesn't pinpoint and a big cloud of either might create a great ball of fire. Did hear some rev increase but couldn't say from where. I timed it to 7* as stated. Turned up the idle to where it would stay running, albeit rough as hell, hooked up vacuum gauge and it's a horrible 12-14 where it once was a good 20. So, that rules out the idle circuit? The carb in general? The remflex gaskets call for some low torque reading, maybe 30 ft/lbs and I have often thought they are a compromise in that they may be an excellent exhaust gasket, something like silicone would be good for intake ports. Maybe I sucked in a chunk of remflex??

 

[island45]

No change whatsoever with mixture screw seated or ready to fall out. After it falls out the top, the engine imediately quits. My wife was calling me in for my cold dinner so I didn't listen for the solenoid click yet,

 

[77mustard40]

Sure sounds like a big vac leak, spray carb cleaner at the base of carb and all around intake and exhaust manifolds to see if the idle pics up. Pics of the engine bay may help the community solve your problems