Inliners International Forums General Discussion Engines Momentary Jerking

On my 250, I recently resealed the manifolds' gasket, rebuilt the carb, new points cap rotor and condenser but for some reason it jerks momentarily when I'm cruising on the highway.

As I'm driving, it feels like the spark cuts out for a split second and like 2 of the cylinders don't fire or something. This causes it to jerk a little and it's not very comfortable. It happens randomly but usually once or twice every 6 seconds or so. I don't feel it during first and second gears (but that doesn't mean it isn't happening).

My only thought is a bad coil that doesn't supply a spark for those brief moments. It can't be any of the distributor parts because those are all new and I set them to factory except for the timing.

Any thoughts?

What is the gap on your plugs? Did you set the point by dwell or by gap? Tom

Might be a lean misfire at cruise.

Oh wow. I set the dwell to 33* and then regapped to .035". I never went back to check the dwell after I regapped the plugs...

Ooops... I'll check it tomorrow.

And I don't understand how it could be a lean misfire. Would the mix stay correct as soon as it got off idle? Isn't the only mix that you can adjust (therefore adjust incorrectly) the idle mix?

Gapping the plugs at .035 is good, this will not affect the dwell.
You may have debris in the high speed jet.

How are your plug wires? Coil?

The carb should give richer mixture for acceleration, then leaner at cruise if it's working right.

If you have a vacuum leak, for example, the extra air may not cause a lean condition during acceleration because you have more fuel already plus the vacuum is less so it sucks less air through the leak. Result is runs well when accelerating but misses at cruise.

I'm not saying this is your problem, just that it could be.

If it goes away when you accelerate with light throttle, it's lean mixture or (possible) too much vacuum advance.

Did you change the spark plug wires too? A bad plug wire will cause a miss like that at cruise.

Alright, I set the dwell from 33* (it hadn't changed since I regapped the plugs) to like 26* and I couldn't tell a difference because my dad wouldn't go on the highway today. It started pinging though so I need to redo the timing. I checked all the wires for resistance and the short ones were less than 3k and the long ones, less than 6k so they're all good. I don't know how to check the coil to see if it's good. I blew out all the passages well and soaked all the pieces so there shouldn't be anything in the carb that's messing it up. I'm still confused as to why the best mix is all the way in. Any ideas?

Thanks

Put some (Xylene) 117 octane to stop the pinging ;).,,, from Home depot or other chemical or paint stores in your tank.
Much cheaper than to buy those octane boosters,plus it will raise your octane higher than those $8.00 a can store bought ones.

Just be carefull not spill it on you or plastic parts.

Many people have used it w/great results. I have also.

Here are the ratios: http://www.gnttype.org/techarea/misc/octanebooster.html

Disclaimer: Use it at your own risk. The Organization is is not responsible for any damage or problems associated with use of this information.


MBHD

Did you say that your best mixture setting is all the way in??

If so, you've got something wrong with your internal carb adjustments/settings.

If I misunderstood that, then check your dizzy for shaft slop. I had an old sloppy one on my 230 last year that worked fine when I was accelerating, but under light loads it would cause a random miss. Changed the dizzy and all is well.

Kirk

Yes, That's right. I've rebuilt the carb twice and I double and triple checked everything the second time. I blew out all the passages, soaked it, reassembled with a new rebuild kit and everything.

Like I said new distributor parts but never check the shaft for play though.


The pinging is from it being too advanced and just general timing/dist problems. I know that high-oct would probably help but 8.5:1 shouldn't need anything but 87 from the pump

I just took out the back glass today and will be taking the front out soon. Need to repair and reseal the channels. I had leaks in both the front and back.

I won't be driving (therefore testing) for awhile but any ideas on what to look at would still be appreciated