Stutters at wot, 89 2.6L

[Justin90gsx]

Ok the truck is super clean, runs great, but when I give it more than half throttle it hesitates and bucks and goes but is weak.
I think it may be something with the big jet cause I watched the idle jet just drip like it's supposed to and the mid spray really well and the big one kind of trickle?
But has new cap, rotor, plugs, wires, timing set to stock, air filter and fuel filter.
And I ran two tanks treated with Lucas fuel treatment. The truck runs perfect!
Besides at more that half throttle, and only twice it ran great for a min.
Is there valve that could stick inside the carb? Or scrub the jet?
Thanks!

[Andy 2]

The Mikuni card has a mechanical secondary. Perhaps there's not enough fuel getting through when it opens and it leans out too much.

[Justin90gsx]

Well I don't know much about carbs unless it's on a 4 wheeler.
Is there a diagram I can look at to see what needs cleaned?

[ragragtimetime]

defective spark plug, defective coil wire or coil, vacuum advance leak or mechanism issue, fuel pump worn, leak in fuel line/fittings, restricted fuel filter/pinched feed line....pull the new plugs & see if they give any clues.

[Justin90gsx]

It is the original coil

[Justin90gsx]

Wondering if it's just tired and needs replaced

[ragragtimetime]

my past experience a bad coil causes idling issues & poor acceleration...based on your info my guess is its not your coil...but if it is http://www.rockauto.com/ & use:
2098355618842663 for discount good til may 25th

[Justin90gsx]

I wonder if the carb is still just gummed up? And maybe run some sea foam threw it.

In 6 months to a year I plan on swapping in a 2.4L and dohc turbo, I already have the block and a complete running donor car!

[camoit]

Change the fuel filter.. It's been 30 years and it need a new one. It's plugging up.

[Justin90gsx]

I listed that I changed it,
And it looks like it was done a year or so ago to when I did it.

[camoit]

I listed that I changed it,
And it looks like it was done a year or so ago to when I did it.

Well next is the coil and fuel pump, Then comes the needle and seat and float adjustment. Aafter that comes compression and valve adjustment.
But you might have picked up a load of dirty fuel. You never know.

[Rickdees]

In your night rail road jump test video when I watched it heard it sputter. . ALL the articles I've read say the 4.3 loves to breathe and you didn't mess around in your build. Remember I'm running a 500 cfm. I say it's lack of fuel and it's sucking the bowls dry.
The only time I heard it is when you were in high gear and WOT and when you backed off it stopped. Fuel.

[camoit]

In your night rail road jump test video when I watched it heard it sputter. . ALL the articles I've read say the 4.3 loves to breathe and you didn't mess around in your build. Remember I'm running a 500 cfm. I say it's lack of fuel and it's sucking the bowls dry.
The only time I heard it is when you were in high gear and WOT and when you backed off it stopped. Fuel.


I think you got this thread confused with my truck. But what you herd on my video is just rough road and me lifting my foot for road conditions and safety. It's not that great of a road unless you in my truck then it's fun. But a regular car it's rough and full of pot holes.

Sorry we aren't trying to thread jack you.

[d50dave]

My truck had the same problem. I replaced the carb with a lifetime rebuilt from national carb. Runs fine now.

[originalowner]

Ok the truck is super clean, runs great, but when I give it more than half throttle it hesitates and bucks and goes but is weak.
I think it may be something with the big jet cause I watched the idle jet just drip like it's supposed to and the mid spray really well and the big one kind of trickle?
But has new cap, rotor, plugs, wires, timing set to stock, air filter and fuel filter.
And I ran two tanks treated with Lucas fuel treatment. The truck runs perfect!
Besides at more that half throttle, and only twice it ran great for a min.
Is there valve that could stick inside the carb? Or scrub the jet?
Thanks!

The symptoms you describe are screaming CARB and it's only a matter of time before that Mikuni lays down and won't get up. The main body of the carb is plastic (bakelite) and the throttle blade shaft wears it out- to the point where there is a severe internal vacuum leak inside the carb.

If it runs OK until the underhood temp reaches max then I would bet that is your problem. That's how mine played out.

[geezer101]

First - test the secondary vacuum throttle shaft actuator (the prime suspect in midrange to top end power loss). Check all the top cover screws and the main mounting bolts to see if they're tight enough. Give the outside of the throttle plate a squirt of WD40 etc while it's running and see if there is a change in how it runs. If it improves for a second then you have a leak somewhere. If not then try this - with the air filter off and engine running get a buddy to keep the throttle open, cup your hand over the throats to try and starve it of air (not completely to stall it but enough to choke it), This might be enough to purge any debris in the jets and improve how it runs. Good luck!

[pennyman1]

make sure the hoses going to the box on the drivers inner fender are good - usually critters get in the box and eat the hoses, or the hoses rot and split - it will show up around half throttle as a vacuum leak.