Hesitation on Acceleration with Trollhole Carb (1 Viewer)

[GeologistFelix]

Ok, so, I've got my desmog pretty much finished, but it's not running right yet. When I give it throttle too quickly at idle (or while I'm moving), it hesitates and stumbles/sputters before it revs up. If I apply throttle gradually, it revs just fine.

Here's what I've checked so far:
- Set the timing to stock, as well as advanced about 3 degrees past stock (without any pinging problems)
- Checked the vacuum. It's pulling 20psi consistently at the manifold at idle. When it hesitates, though, it falls to zero vacuum for half a second while the engine is bogged down/misfiring/whatever it's actually doing.
- Checked the vac. advance on the dissy. It moves like it's supposed to when I pull a vacuum on the main advance port.
- Adjusted the idle mix, both via tachometer and vacuum gauge. I don't think I have it quite right yet, but I've set it both on the lean and rich side, and it hasn't stopped the hesitation.
- The fuel level in the bowl seems slightly low (i.e. right at the top of the bottom 'arrow' on the sight glass)

For those who don't know, the Trollhole only has provisions for the vac. advance, and Evap by way of the inlet on the insulator plate, and the evap pipe that goes into to the (former) EGR inlet port on the manifold.

For what it's worth, it seems to do better when warm, but it still has hesitation problem.

Here's what I'm thinking it might be:
- Something is wrong somewhere with the ignition system, like maybe the electronic part of the dissy, or the coil?
- It starves for fuel temporarily when the throttle is applied too fast, because...
-- There isn't enough fuel in the bowl?
-- The fuel filter is clogged?
- There's an intake or exhaust leak that only manifests itself when the throttle is opened too fast.


Anyone have suggestions about how to narrow things down?

 

[BRUIN4]

I would start with the fuel lines first because thats the easiest - filter for sure! I had the same problem with my Webber and when i yanked it off to rebuild it it was a simple factory installed re-usable fuel filter inside the carb that was 90% of my problem.

What fuel pressure is recommended for your carb? An in line fuel pressure regulator is a simple solution to regulate the pressure off the fuel pump into the carb.

After that I would recheck the vacuum and the ignition - are you running a points distributor?

 

[GeologistFelix]

Stock FJ60 dissy, as recommended for the Trollhole.

Now, how should I go about checking the fuel filter? And, for that matter, the fuel pressure? I have a fuel pressure gauge, but I don't recall seeing any 'test' ports to check it on like my old Heap with EFI did.

 

[EWTexas]

I had this when I did my Thollhole but after I checked my adjustment on the accelerator pump and the secondary throttle valve it went away and has ran great since. So check all the adjustments and see what happens

 

[GeologistFelix]

Wait, how do you adjust the accelerator pump? Is that something I can fiddle with in the throttle linkage?

 

[EWTexas]

You need to get a book, even a Chilton's has adjustment instructions for the carb and these are so close to OEM that it works,it did for me. I set it up like OEM and all the trouble went away. But check out that low sight glass, could be your cause, ie adjust float.

 

[GeologistFelix]

I have the whole 2F FSM. I never saw anything about adjusting the accelerator pump in the carb section though.

 

[GeologistFelix]

Looked in the FSM, nothing. Looked on the web, learned that you can bend the linkage, and that the pump shaft is supposed to have a 9.5mm stroke for the 2F carb.

Time to go fiddle with it, I guess.

 

[EWTexas]

Sorry I'm old school, I check how much gas comes out when lingage is moved and bend arm to increase or subtract to where I like it. But from my book" Check that the length of the pump stroke(length that the pump lever travels) is 9.5mm for 2f. If it is not, it can be adjusted by bending the connecting link".
The lever they are talking about is the flat arm that pushs the acc pump valve down into carb, check this as you work lingage and measure at the top where lever joins the pump valve rod. But check ALL adjustments like slow and fast idle because they will affect what the out come is. Also check the secondary throttle valve adjustment, if it opens too soon it causes a need for more gas.

 

[Heartworm]

There is a little screen in the Aisin carb where the gas line enters. That sucker can get clogged. Might want to check that too. But I agree, the accellerator pump is suspect.

 

[GeologistFelix]

Update!

Measured the accel pump stroke, determined that it was only about 2/3 of the 9.5mm it was supposed to be, and put in a nut as a spacer, which happened to be just the right size.

Now it only hesitates if I really slam the pedal down when the engine has just started from being dead cold, which I couldn't care less about. The rest of the time it's running like it should.

 

[snowbound1975]

Nice macgiver tactics

 

[GeologistFelix]

The rod in the linkage was so stiff that I was worried I'd do some damage to myself or the rest of the linkage if I gave it enough muscle to actually bend. If I really wanted to do a perfect job, I probably would have pulled the carb so I could rotate the rod enough to get it out of the linkage, then bent it carefully in a vice...but that's a lot of work if you don't know what the problem is.

One thing I have noticed is that, in motion, the torque seems to max out at only maybe 3/4 throttle. If I were to hazard a guess, it may have something to do with my dissy having the stock curve, and that a recurve from Jim C. would get me some oompf out of that last bit of throttle. Either that, or my secondary isn't opening all the way or something?

I'm not really in any hurry to fiddle with it too much now, though, since it's running smoother, starting/idling better, and pulling harder than it ever did with my old carb.

 

[jfnall]

Update!

Measured the accel pump stroke, determined that it was only about 2/3 of the 9.5mm it was supposed to be, and put in a nut as a spacer, which happened to be just the right size.

Now it only hesitates if I really slam the pedal down when the engine has just started from being dead cold, which I couldn't care less about. The rest of the time it's running like it should.

Where did you put the nut on the accelerator linkage, on the firewall side of the lever? Above it? Just trying to envision this. I'm having the exact same problem.

Might have up look at the secondary adjustment. Is the secondary adjustment something that a change in the linkage will fix like the accelerator pump?

 

[worldspan]

More details please

Where did you put the nut on the accelerator linkage, on the firewall side of the lever? Above it? Just trying to envision this. I'm having the exact same problem.

Might have up look at the secondary adjustment. Is the secondary adjustment something that a change in the linkage will fix like the accelerator pump?

x2 on where you put the nut....?

I'm having hesitation issues as well and some have mentioned the Acc Pump but I'm not sure how to 'adjust' or measure the stroke of it. Any more details and/or pics would be fantastic.....


Thanks

 

[Ry24000]

Wow this link went dead without a solution!!! BS...man. I'm having the same issue and I am reluctant to post a new thread for fear of backlash of the "do a search" crowd. I don't post on forums often, but when I do I always post a solution to the origional problem!

 

[OSS]

I am reluctant to post a new thread for fear of backlash of the "do a search" crowd.

The “do a search” crowd can pound rocks. The FJ60 forum is pretty quiet nowadays with rarely any new threads. It’s amazing that guys who can barely lift a finger to type out “do a search” had enough strength to open the link in the first place.

These are the things that annoy forum contributors to the point where they give up and don’t want to get involved:

Original Poster:

1. States a very vague symptom with no back story or details. Example: “Engine runs bad”
2. Expects forum contributors to play 20 questions to get a handle of what’s sort of going on instead of stating the details initially in the thread
3. After 2 pages of questions by other members, OP finally reveals all the hacks and changes that he’s made to the vehicle which usually means the problem is not diagnosable on a forum.
4. OP provides three word responses to questions from other members

There’s lots of people here who enjoy troubleshooting these vehicles and they’re very good at it. We’ve seen all these problems before and many of us know the symptoms and causes. For some of us - troubleshooting a problem on this forum is fun and rewarding when a suggestion ends up being the solution to the problem.
When it becomes a drag is when the OP isn’t helpful. That’s when we bail.

So my advice-
Post a new thread when you’ve got a question.
And don’t be afraid that it’s a “dumb” question or “newbie” question.

There’s threads here asking how to check the motor oil. That’s fine.

 

[Spike Strip]

Wow this link went dead without a solution!!! BS...man. I'm having the same issue and I am reluctant to post a new thread for fear of backlash of the "do a search" crowd. I don't post on forums often, but when I do I always post a solution to the origional problem!

Most threads end without a resolution as posters are usually just looking for a quick fix and then, when they find it, just get on with life. It's understandable, and frustrating to be sure. Don't worry about the 'do a search' crowd. Obviously you did as you found a 10-year-old thread!

OSS is spot on. Start a new thread and it's really really helpful to post pictures of your issue and setup. I would strongly suggest a $20/year silver star membership for unlimited postings and no ads. If you own a cruiser and want to learn how to fix it yourself, or at least diagnose, it's a very smart investment.

 

[GeologistFelix]

For what it's worth, the carb is still slightly balky ten years down the line, but reliable, and I have a desmogged Jim C. unit sitting in a box for after I put the H55 in hopefully before too much good weather goes by.

I'm willing to chock any weirdness, early on, up to me being an idiot 24 year old and not putting the linkage together right, or the PO doing something funky with the linkage which I then had to correct for. All completely non-OEM, jerry-rigged amateur work.

 

[Ry24000]

Thanks guys!!! I think I will get the membership.
I have done a "TON" of research here on Mud over the past couple of years. Most of the time I find the answer or at least get in the ballpark, but its a ton of reading, sifting through hijack posts or pointless comments.
I think topics like carb. or 2F related should go in a forum that everyone(most) should see. This motor spanned over many vehicles and years yet on Mud we have no "Common Ground" forum. Internet searches always point to threads on Mud that's how I found this one.
As far as my hesitation problem I'm thinking Accelerator pump of a vacuum leak.