Trollhole off idle stumble. (1 Viewer)

[HemiAlex]

Just got my trollhole installed. It all went easy except for my fuel cut solenoid being left off on accident.

Here's where I stand :

-air cleaner vacuum lines and ports are capped where needed. Found a pvc vacuum leak that was quickly fixed.

-AC idle up installed.

I'm referencing the attached diagram for setting the idle, but my actron remote rpm gauge is dead right out of the box. So I'm going to the factory tach.

I started at 2 turns out on the idle mixture, kept on turning til the idle wouldn't raise any more. The I used with inner most idle screw to get it to about 750rpm hot idle. Set the AC idle up and it's right at 1000 AC on.

The problem is that I get a very bad stumble off idle. The truck bogs off idle til 2000 and then pulls out of the bog nicely.

I figured that there is a sweet spot in the idle mixture screw that either makes the off idle transition rich or lean. It's that point that I've not reached yet. I haven't tried the idle mixture screw extremely out but so far 1st gear is almost completely useless. I had my factory Aisin set better than the trollhole.

Is there something else that could have caused this stumble that in maybe did in the install? I don't follow what could be that off. I even tried setting the idle mixture screw and idle screw to about the same point that the aisin that came off was at and it didn't help the stumble.

Do I need to call Marshall tomorrow is is there something else going on?

 

[HemiAlex]

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The install guide I followed:

TrollHole Cruisers Carb Install on a 60


I had the aisin running like a champ and it felt great. I've got a good feeling that if I threw it back on, the truck would run great.

 

[HemiAlex]

Also, fuel sight glass is full and I replaced the fuel filter when I did this, even though it was only about a month old.

 

[HemiAlex]

Paging @Tighe

I see you had similar issues. We spoke via pm about two weeks ago...what do you think?

 

[Tighe]

Hey Alex,

I'm no authority on the subject but if memory serves when I received my carb from TH the idle screw was ~4 or 5 turns out. I ended up adjusting this a bit over the next few months, but during that time I never felt there was that much change to drivability. Certainly nothing that I could describe as creating (or solving) a bog, so, with my limited experience I'd say the idle screw is not the right place to be looking. I'd set it at whatever Marshal recommends and move on to the next potential culprit.

I've heard of debris from the manufacturing process clogging jets- this didn't happen to me but may be worth investigating. Have you tried removing the air cleaner and putting your (gloved) hand over the carb until it almost dies, then releasing? I've heard doing this a few times can help clear the carb. Again, no first hand experience with this.

When I bought my truck it did have a significant bog at certain RPM's which I troubleshot for a while. First item I replaced was the donut gasket between the air filter and the carb. Make sure this is intact and seated properly. This helped a bit but it still bogged under load. I found that pulling the choke out helped a lot. Eventually I realized the timing was off and as soon as I got that dialed in the bog disappeared and acceleration was smooth.

When you swapped carbs did you look to see if the inside of the manifold was cracked?

Have you sprayed around the carb base with brake cleaner? Assuming the carb was the only item you replaced, check for leaks at any related vacuum lines. Spray around EGR. Watch that hot manifold!

Have you disconnected the ICS to see if it runs without it? If so maybe it's an indication of something awry in the carb. Any visual clues with the carb? One of the linkage arms was bent when I received mine, which I had to straighten. Maybe throttle linkage is getting bound up/kinked? When you rev it by hand does the linkage move smoothly? When you rev it by hand and watch the sight glass, is there a drop?

Of course don't rule out coincidence too...could be something totally unrelated!

Sorry couldn't be more helpful/precise- when I installed my TH it was part of a complete desmog so there were many variables changed at one time, which made pinpointing issues difficult. See what Marshal says and report back, curious to see what the verdict is.

 

[HemiAlex]

I have to give a huge shout out to @Trollhole
Marshall spent over an hour on the phone with me today in order to troubleshoot this install. Once I pulled the idle fuel circuit he verified that the idle circuit was working properly and he worked through the other possible issues. Carb wasn't at fault.

I feel that I rushed the install. I got some of the mess of vacuum hoses messed up and that really made things badly. After it barely ran this morning, one by one I started by plugging all the vacuum ports completely.

I removed the carb completely and cleaned the mating surface. Then retorqued the carb. I then checked for leaks at the intake and vacuum sources and I finally had it sealed up. No issues. When it started I had to re do the lean drop idle adjustment. It's now running at 750 with a perfect idle.

I need to advance the timing and I feel it will be 100%. I'm going to shoot for 9-10 degrees.

I have to say, it starts like an EFI truck now. .5 second and it's running without pumping the throttle or holding it down.

We will see what the long term is for this carb, I'm still planning on sending my Aisin to JimC for a refresh to keep on the shelf. If this troll hole pick up even 1mpg average I'll be completely happy.

 

[roadstr6]

I like Trollhole's carbs. I run them on both my cruisers. If smog isn't a concern you can't go wrong with them.

 

[Trollhole]

Thanks for calling me. And you got lucky I had the time. But I had just literally read this post and was writing a response when you called.

As far as the batch of carbs with debris. This was 3 years ago and was isolated to maybe a dozen carbs out of one batch. I'm over 3400 carbs sold in the world now. I think I have a good grasp of what works and what doesn't.

 

[MicahMan]

I'm over 3400 carbs sold in the world now. I think I have a good grasp of what works and what doesn't.

Understatement! I've bought 5 carbs from Marshal all work great after I adjusted them and got timing dialed in for my Elevation. Can't beat em they are a dynamite product. There is even one on a spotless restoration that hangs out in a museum.

 

[gregnash]

Yeah one of the things that is on the "fairly short list" once I get a welder to clean up some body stuff.

 

[HemiAlex]

@Trollhole

Can you break down the timing spec for me again?

 

[Trollhole]

I like it at 9-10 degrees. 3/4 to the bottom of the window.