Adjusted choke, now engine runs bad

[deebee53]

Ok, my car was running nice with the exception of it staying on fast idle even when hot. I adjusted the choke and now it runs like a dog . . .

The details: 200 out of a '67 Mustang with a L-O-M dizzy (with electronic ignition) and a 1100 carb.

I hooked up my wideband and just off idle it starts to run really lean (17-20) and isn't happy about it. Under acceleration its in the low 16s and has no power.

I checked the float level and its right on. So is the accelerator pump adjustment. The main jet is a 68. The choke is wide open when hot. The hard fuel line was in contact with the heater hose during this. I isolated it with a piece of hose, but this was after it already started doing it.

Also, it idles at around 13-13.5. More rich or more lean and it doesn't run as nice. It has always idled rough both before and after this problem.


The thing that confuses me so much is that it was running great with plenty of power (come to think of it, it would start running like this after awhile of driving).

I am going to run a new fuel line so it is not in contact with anything else. Any other suggestions?


P.S. Sorry for the long first post here. I have been searching for awhile on here though. Great information guys and I appreciate the help.

 

[fordconvert]

Are you sure you were adjusting the right stuff? Was your choke open all the way before when it was running alright? How does the idle screw respond?

 

[deebee53]

I'm not sure where the choke was before when it was hot, but I would rev it a couple times and kick it off fast idle then start driving and it would go back up on fast idle. I adjusted the fast idle screw and the choke housing because the choke was staying partially closed for a long time after it was warm. Maybe the choke was getting pulled partially closed under acceleration and making the A/F rich? That would help explain why I'm lean now.

I adjusted both the idle speed and idle enrichment screw incrementally until it was running the best. This came with a A/F of around 13.0.

Is my main jet too small? It doesn't seem like it should be, but you guys would know better than me . . .

 

[BIGREDRASA]

Not the expert on 1100s, but sounds like you need to go back over every step of setting up the choke. Start from scratch. When all is OK, suspect the Power Valve, except I don't see one in my diagram.

 

[deebee53]

Well, I can look at the choke wide open when its running bad. Plus, its running way lean so starving for air isn't my problem.

I have the old carb from the 144 and stole the power valve off of that one, but it had no effect on the way it was running or the A/F.

Thanks for the replys, please keep them coming.

 

[page62]

I'm gonna throw a wild pitch here...

Your choke probably wasn't opening fully before you fiddled with it. So you had a richer mixture at all times. By making the choke work right, you leaned out the mixture.

You probably need to rebuild the carb. For starters. Then we can discuss messing around with the main jet...

 

[fordconvert]

The 1100's the power valve is pressed into the top cover casting and all the books say 'do not remove'. The thing that looks like a holley power valve is the spark control valve.

 

[deebee53]

The 1100's the power valve is pressed into the top cover casting and all the books say 'do not remove'. The thing that looks like a holley power valve is the spark control valve.

Hehe, yeah my dumb brain didn't realize until after I posted what I had replaced . . .

I did some more checking last night with some starting fluid and my wideband. I'm almost positive the base of the carb is leaking. I replaced with a new gasket I made, then with an old gasket I had. The old gasket was thicker than the one on there and made it run slightly better. I'll get a new gasket then let everyone know how I make out.


And . . . yes, the choke WAS staying on and artifically richening my fuel mixture. I closed the choke with my hand and it ran alot better.

 

[deebee53]

Ok, so I ran a file across the base of the carb, and the mounting plate to get them both as straight as possible. Then I made a cork gasket to seal it up.

Now it runs good at idle and great off cruise. WOT a/f is around 12.6-12.8 so its real happy there. The only thing is just off idle and during cruise when the throttle is just slightly open it runs about 16.0 a/f and breaks up.

I don't want to rejet it because I like my WOT a/f ratio.

Any ideas as to what is causing this and how I can fix it?

 

[ludwig]

Is the carb clean inside and out? The transition circuit might be dirty, like partially blocked. Make sure the port that draws the warmed air though the choke pull off spring is clean and not blocked and that all the linkages are sliding freely.

 

[deebee53]

Is the carb clean inside and out? The transition circuit might be dirty, like partially blocked. Make sure the port that draws the warmed air though the choke pull off spring is clean and not blocked and that all the linkages are sliding freely.

The carb is clean on the outside and it looked pretty clean when I had the air horn off.

I will take it apart and re-clean it anyway.

 

[ludwig]

Blow out the holes with compressed air. If you don't have a compressor, use a can of pressurized air for cleaning computers. Office Depot or wherever.