Help with Diagnosing FJ60 stumbling / bucking

1973Guppie · 11-02-09, 08:32 PM

Hi all, I am working on an fj60 right now and was hoping some can give me their thoughts on what they think the issues are that are causing these symptoms. This is a florida truck in CA and it has been basically raped of all the smog equipment. I will be replacing the intake / exhaust gasket, new rebuilt carb installed, and all smog equipment reinstalled and hooked up.

Symptoms: the engine seems to run strong. I still have to do a compression check on the block to make sure everything checks out ok. Basically, after starting, and after warming up for a few minutes the vehicle bucks wildly upon acceleration and deceleration, the bucking is much worse under load (uphill/gas) and going downhill in gear (engine compression), it seems much worse over 2k rpm's. It seems to have a high idle as well. I am thinking the desmogging of this car was not done right and there is major vacuum leaks. I could not find any major vacuum leaks in the intake/exhaust manifolds. Under load the bucking is very major, like fat albert is humping the rear of the truck. Basically it feels like somebody is turning the gas stream ON/OFF/ON/OFF, if that makes sense.

I am thinking it is a combo of vaccuum leaking and something going on with the existing carb? the owner said they purchased the carb on craigslist and they said it was rebuilt but to me it does not look very good whatsoever. This whole engine basically needs a once over. Owner also said that the fuel filter was replaced, but am also wondering if there is sediment in the tank causing a lack of gas / blockage, but that would not make sense since in low rpm's and for the first few minutes of running it seems to run just fine. Valves also sound like they need adjusting.

here we go.

thanks for the help and opinions, I am sure I will figure it out but wanted to get some opinions b4 I start digging into it.

Noah

alaska60 · 11-02-09, 09:16 PM

sounds like your on the right track. You listed all the spots I would check.....could be a fuel filter. when it sits the sediment settles.... once warmed up and fuel has moved the sediment around....it could restrict the flow.?
Check the vac lines for cracks....
when all else fails send the carb to JimC.

1973Guppie · 11-02-09, 10:43 PM

thanks for the help, appreciate it, what make me think it is not the fuel is that it is not intermittent, the bucking is almost on an even repetition, especially when backpressure is applied (engine braking) downhill, as if as the engine cycles it hits a point and causes the stumble. The more I think about it, maybe the valves are grossly unadjusted? would that cause this? hope so, that is an easy fix.

I am sure the problem will arise as I gut this sucker out to find the problem....

wengejor · 11-03-09, 06:47 PM

I had some bucking problems over 3K rpm and it turned out to be the fuel filter. After that it's been smooth. I now have an extra one in my travel pack.

1973Guppie · 11-03-09, 08:15 PM

yes, that was the first thing I thought of to be honest, owner said it has been replaced but I am thinking it may make sense to replace it again and drain / rinse the tank out thoroughly as well to ensure there is nothing going on inside of it. Usually if it is a sediment problem you can tell after pulling the fuel filter and tapping it on concrete to see what comes out. If there is rust particles his tank will have to be looked at closer. I will probably start with the engine and make my way back. No way I am starting the truck back up with the new carb without a new filter, checking the tank and blowing out all the lines.

Noah

alaska60 · 11-03-09, 08:33 PM

Good call!
GL......

digby · 11-15-09, 12:25 PM

On a semi-related note, where is the fuel filter located? I can't seem to find it on my 1984 FJ60...

RogueBetty · 11-15-09, 01:43 PM

Quote:

Originally Posted by digby

On a semi-related note, where is the fuel filter located? I can't seem to find it on my 1984 FJ60...

passenger side of the engine it is in a clamp on the wheel well behind the ac res.

Mine was doing that I adjusted the carb, never had been adjusted before still had the cap over the mixture screw. And re-timed it. Doesn't buck now.

NLXTACY · 11-15-09, 03:04 PM

My issue was not a fuel filter so much as it was really old fuel lines. One line in particular, from the filter to the pump, was gel'ing and peeling off in bits and f'ing up the carb causing some of the things you mentioned. I just took out ALL the rubber lines, went to AutoZone and replaced them all, cut to length, for under $30 and it took me all of half an hour to replace them all. And of course replaced with a new TEQ fuel filter to boot.