Rebuilt Carb = Inconsistent Engine RPM

[Jetlander]

All,

I rebuilt my 77' Aisan Carb for a 2f motor a few months back and during the rebuild I found the accelerator pump retainer peened shut, I carefully filed out the peening to free it up. Overall the 40 ran pretty well after the overhaul. However, about a month ago it refused to idle and would stall. I replaced the carb idle solenoid and the problem went away... for a few weeks. The gound for the idle solenoid is good and I can hear it operate when I turn of the 40.

Anyways...

Now if the RPM gets anywhere near 1000, the engine wants to die. At 1500 rpm it will run perfect, but seems rich. I have tried everything to figure it out and no dice. To top it off, I adjusted the fast idle to 1500 rpm with half choke. The next time I start it, the engine runs at 2000 rpm with the same choke setting. Overall the engine rpm doesn't ever seem to stay consistent, always wandering about 200 rpm. I'm getting super frustrated because I can't seen to keep it running long enough to make any more adjustments.

FYI- The fuel in the bowl indicates dead center of the sight glass.

What could the problem be? As of right now I'm about to give up and buy a trollhole carb and call it a day.

 

[Splangy]

If everything else with the engine is fine, it sounds like it won't run off of the idle circuit. So, that means your idle solenoid isn't working, your idle mixture is way off, or you have a clogged port in your idle circuit.

 

[Jetlander]

If everything else with the engine is fine, it sounds like it won't run off of the idle circuit. So, that means your idle solenoid isn't working, your idle mixture is way off, or you have a clogged port in your idle circuit.

That's the thing, I don't think the idle mixture is "off" as it is about 1 1/4 turns out. The idle solenoid is new and it can be heard actuating when I put power to it.

What would drive the inconsistent idle speeds each time it is started?

 

[Splangy]

It's unlikely to idle smothly if there's fuel flowing down the venturis and not through the idle circuit. Keep in mind that 1500rpm is not an idle. Your carb is using the primary fuel circuit at that point and not the idle circuit. You need to figure out what's wrong with your idle circuit.

Just because you hear the click doesn't mean everything is ok. The rubber o-ring could be damaged. There could also be something plugging up the idle circuit.

Are you sure you don't have a vacuum leak somewhere?

 

[snaggletto]

Agreed. I had a similar situation. I removed idle solenoid and sprayed carb cleaner through the hole it was removed from. Check the condition of the oring at the end. Also, I removed the fuel screw, (valve cover side) and sprayed carb cleaner through that hole. Make note of screw turns out from lightly seated, tightened down hard will damage the brass needle. Should see carb cleaner shoot into carb mouth when spraying through either hole. Wherever the trash was. These two things cleared it out.

 

[Pin_Head]

Manifold vacuum leak?

 

[sggoat]

I would vote idle circuit issue--a vac leak should be (for the most part)consistant- doesn't seem to me it would vary as much as you are experiencing-usually, a constant leak should depress rpms(although, there are some things that will cause varying vacuum--like a leaking pcv valve-)

 

[FJ40Jim]

A 77 carb idle jet is a little too small. The idle mix needle should be 4 turns out to get least bad idle quality.

 

[Jetlander]

I would vote idle circuit issue--a vac leak should be (for the most part)consistant- doesn't seem to me it would vary as much as you are experiencing-usually, a constant leak should depress rpms(although, there are some things that will cause varying vacuum--like a leaking pcv valve-)

You've hit the nail I think. What I've been fighting is inconsistent rpm. I can adjust the rpm and the very next time it seems to be different. The accelerator pump was peened when I took it apart for the rebuild. I carefully filed the peen out and thought I had done a good enough job to prevent it from catching, but now I'm wondering if perhaps it's hanging up? Regardless, I've ordered a trollhole because I'm beyond frustrated with it. Once I do the swap out I'll probably send it out to be rebuilt by someone more versed than myself. Having a spare wouldn't be a bad idea.

BTW, does anyone have a link for a good electronic dizzy? I'm thinking of simplifying the entire system. Not having to worry about points anymore is looking more appealing.

 

[Jetlander]

A 77 carb idle jet is a little too small. The idle mix needle should be 4 turns out to get least bad idle quality.

My idle mixture is at 1 1/4 out. It ran perfectly there since I rebuilt the carb almost 4 months ago.

 

[FJ40Jim]

There's obviously a problem there. Maybe the end fell out of the idle jet? It happens.

 

[Pin_Head]

Maybe you have an inconsistent piece of dirt banging around in your idle circuit.

 

[Jetlander]

Here is a video about the inconsistentancy I've been seeing. I know the idle is too high, but she will not idle lower without stumbling. If I rev the rpm's to 2000ish and stop, it slowly decreases to 1700ish, holds for a second or two and then stumbles her way down to 1100-1000ish. If I make any adjustments it continues to wander around. Additionally, the exhaust smells super rich

 

[Pin_Head]

Video?
If you smell gasoline, it is misfiring. Carbon monoxide is the product of running rich, not HC. CO is odorless, so you can't smell it.

If it won't run below 1000 RPM, it is not idling, it is running off the main nozzle. This suggests a lack of idle fuel or a large manifold vacuum leak.

 

[Jetlander]

 

[Jetlander]

Not sure why I can't get it to upload, so hoping it can be viewed via FB.