The old girl has this little problem. When running a STEADY speed say 60mph for a period of time, She starts to backfire, and sounds like its running one 1 cyl. I roll off the throttle, hit about 45mph, and she takes right back off just fine.

I don't have this problem on the twisty's where I'm on and off throttle all the time. But highways are impossible to maintain a steady speed.

I've talked to many different people, and gotten many different answers, from valves to electrical to carb. Any of your input would be appreciated. Thanks

 

Could be a fouled plug. Bad plug wire. Coil could be bad.

 

wouldn't it backfire at idle then as well? at least pop some? She idles fine, runs fine for the most part. Just holding a steady speed is the problem.

 

Main jet cloged with trash? Have you had the carb cleaned?

 

carbs been cleaned and rebuilt.

A little history on her. Bike was pretty rough when i got it. Didn't run, was filthy and the aluminum was all corroded. Picked it up for 2 grand though, with 11 thousand original miles. Thought that was a good deal.

Anyway, found the problem why it wouldn't start. Battery ground was hooked to the wrong spot. Fixed that and a little gas in the carb got her fired up.

Then found out the clutches were shot. After about a month waiting for a shop to get that fixed, got her back, and she ran ok. Rebuilt the carb and she ran ALOT better. (accelerator pump was shot) but still doing the backfiring thing.

Got about a weeks worth of polishing on the old gal, re painted the tank and she's looking pretty good. Still a work in progress, and when i figure out how to post pics on this site, I'll throw em up.

I do have a Clymer manual for it, and have been learning as I go. But I'll take this old harley over the honda I had any day. [sm=icon_cheers.gif]

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Check your gas cap vent. If it's clogged, your carb will not get enough gas at constant highway throttle settings. Back off, or run at varied throttle settings, and the gas supply can catch up and it will run well again. Here's a test - with a half tank of gas (so gas doesn't slosh out), get out on the road at 60 till it happens. When it does, open the cap while still doing 60 and see ifthe engineclears up in a few seconds.

Could also be a clogged jet or petcock, but from your description it sounds to me like fuel starvation of some sort.

 

I'm leaning toward a lean condition as well. Not sure who did the work, but I've got drag pipes, no baffles. Also a non stock air cleaner that looks as though it would take alot more air.

I also checked out the tech area here. Theres a thread on how to tell if your lean or fat.Says run her up to about 60 or so and back off the throttle about 1/8 to 1/4, and if the bike accelerates, your lean. Well sure enough, my bikes always done that.

Just pulled the carb and cleaned it, removed the main. Its a 160. Now the big Q.. How much bigger to go?


BTW, this forum kicks ***.. TONS of info here.

 

I'm running a Screamin' Eagleair cleaner (K&N filter), slip-on Dyno-Power mufflers, and choke plate removed from the carb. A 170 works for me. I've used a 175 with a velocity stack and open pipes, but that's probably too big for most fairly stock setups.

 

well i put a 170 in it, and also adjusted the float level according to the book. Runs like a dog on top now. Lay on the throttle over 50 and she spits and sputters.

Thing is, book says to check float level in "valve fully closed" position. Now it just tells you to hold the carb a certain way, no mention of adding any pressure to seat the valve tight when measuring. I didn't hold it, and adjusted it, and now I'm not sure I got it right. Float level may be too high now, which according to the book will cause poor acceleration.

That i really would like to know before i go down to a 165. Dealer told me 160 is stock, so with pipes and a different air cleaner, it should have been fattened up. Plugs look a little lean if anything.

 

If the problem is the same or worse with a 170, then a 165 won't help. Maybe the float level is off, as you say. Did you check the gas cap vent and petcock? Has the inside of the tank been coated with something that's coming off and clogging the petcock? Kind of hard to diagnose over the internet, and I'm no mechanic, either.