rapid misfire/bucking at Hwy speeds

[Pandaram]

i got a 88 2.0 5 speed 4g63 and i just replaces cap and plugs(wires still look good and seems to have a new rotor) when i give it full beans it bucks and sputters i'm fine if i stay around 65. only seems to do it on the freeway any ideas on what it could be? i'm kinf of new to the carb world and i think i still have the stock carb(vac lines everywhere) any help even linking to a thread i missed in my search is appreciated.

[geezer101]

I think you will find it's not the carb but the ignition tune. If it's running rich/running on from overfuelling that will be the carb. The factory specs for ignition tuning nerf these engines badly. If you have a timing light and a dwell/tach meter you can try this - use the timing light to set your base advance, then get someone to hold the engine @ 2,000 rpm and adjust the distributor by gently swing it back and forth until you hit a 'sweet spot' and the engine rpms jump by themselves, then retard the timing just a touch (this will act as a buffer for the engine not being under load and as a precaution for crap fuel). You don't drive @ idle rpm so the engine isn't tuned to run at it's regular cruising/gear shift rpm. It will slightly affect the engine at low rpm but will make hill climbs and freeway driving a lot more friendly.

[camoit]

Have you changed the fuel filter. After 30 years they tend to get plugged and not flow enough at speed.
You will find that under the bed by the tank on the drivers side.
Also at that speed you need to look for emission side vacuum leeks since that is doing it;'s thing at speed also.

[geezer101]

Have you changed the fuel filter. After 30 years they tend to get plugged and not flow enough at speed.
You will find that under the bed by the tank on the drivers side.
Also at that speed you need to look for emission side vacuum leeks since that is doing it;'s thing at speed also.

...o.k. add that to the list. Forgot to add a tired ignition coil as well. They have a tendency to break down at higher rpm if the coil is 10-15 years old. It will cause power loss and poor fuel economy.

[yamahlr]

Drove me nuts for a while-you guessed it!Ignition coil. Find on flat highways and lower speeds thru the gears etc. Finally stopped by dealer, first thing top mech did was check of coil. Not totally bad but on it's way out. New coil- no more problems. Years later upgraded to Jacobs off road team system,haven'looked back since.

[Pandaram]

thank you guys sorry it took me some time to see this i've been busy. i'm going to replace both the filter and coil since it needs done anyhow.

[Pandaram]

question does anyone have any upgrade suggestions for a ignition coil? i was looking on jegs and there is one for a 86 2.0 would it be the same for the 88 2.0?

[Pandaram]

okay so i replaced coil fuel filter and did the spring mod for the other barrel(it was not opening) it is more peppy but still bucks and misfires. cap and button look to be in good shape timing is about +10 new plugs wires coming in mail anyone have any other suggestions? also cleared the carb(its the stock mikuni) with the rag method.

[geezer101]

I have recommended this tuning method a number of times and have received positive feedback from members who have struggled with ordinary highway cruising speeds and uphill driving. Set your timing & idle rpm to factory specs, then hold the engine rpm @ 2000. Swing the distributor back and forth between advance/retard gently until you notice the engine rpms peak by themselves, then retard the distributor a little from that peak point and lock the distributor in place. It may be a little sluggish off the mark but you should have an improvement in midrange and top end power and the engine will generally perform much better.

[Pandaram]

appreaciate it geezer. my timing is like +10 atm i shall try this after i grab a tach

[pennyman1]

check the hoses going to the box on the driver side inner fender - hoses rot and get eaten and cause vacuum leaks. Box controls the electronic carb and will cause the hesitation and backfiring you describe.