Lack of power

newell

79 Special...
Messages
43
Reaction score
0
Points
6
Location
Fort Dodge IA
So I thought that I got all of the problems with my carbs fixed (79 Special, 2 into 1 exhaust and pamco ignition), having gone through the carb guide 3 times and reseting the float to 24mm, I have almost now power at any point when I roll the throttle, from take off to wide open... any ideas and tips to help get things going in the right direction would be greatly appreciated. cheers
 
Have you run the bike with stock exhaust?
I had a 2 into 1 that came with my bike, didn't like the look or the performance, didn't want to dick with the jetting. Picked up some stock pipes and a world of differerence.
 
got the bike that way, I rode it last season and it had tons of power and I loved it, now it just cannot seem to get any power out of the old girl...
 
Were the carbs re-jetted for the pipe? If not, the bike could have been running too lean. After running a whole season like that, it may be too late, the damage may already be done. The sudden loss of power might be an indication of that. I would run a compression check.
 
As far as I can tell the carbs were not re-jetted... my a season, i got it going in July and rode until august 15th last year and then didn't ride until July this year...any ideas on compression gauge price or manufacturer?
 
So i checked the compression and after 2 kicks, key off it was around 110psi on the left and 100 on the right... plugs were black and looked wet... thanks again
 
Well, those numbers aren't the greatest. To get the best test results, test on a warm engine, open the throttle fully to let air in as you kick, and keep kicking until the gauge stops rising. 2 kicks may not be enough.
 
140 psi on both sides after a ride, and throttle open as per 5twins... seemed to have more power today... I also cleaned the plugs when I took them off... not sure if that would have helped...
 
Well, that's more like it. 150 is ideal but 140 isn't bad. Looks like you haven't killed it yet, lol. That's the good news. The bad news is it isn't running as well as it should. I'd start by going through all the basic tune-up stuff again - timing chain, valve settings, and timing - yes, timing. Even though an electronic set-up is supposed to be "set and forget", many times a few hundred miles after install things can change slightly. I don't know if it's new parts settling in or what but you may find the timing not quite right now.

If all that checks out it may be time to look into the carbs again. Just because you haven't re-jetted, it doesn't mean the P.O. didn't. But if he did, he may not have done so correctly. These carbs, especially the '78-'79 set, usually require a bit more than just upping the main jet size.
 
Next time you go to the parts store buy 2 spark plugs. Put them in and I will wager your problem will magically disappear. Been there. It makes sense to take care of the easy stuff before going in deep, things like plugs, points, timing are simple compared to yanking carbs and messing with jets.
 
Carbs have been synced, I think that King is on the right track, after going though the things that 5twins mentioned... I set the valves and looked at timing... both were good...I am curious why the left side plug is a little "blacker" then the right... i am sure that the previous owner didn't re-jet, any ideas on where to go form stock jets with a 2 into 1 header and megaphone muffler?
 
Your carb set doesn't need much larger mains than stock because it came with the largest main ever put in a 650 (#135). Try one or two sizes up (137.5 or 140). Because of the large stock main, the upper midrange is right on the verge of being too rich. Just about any increase in main jet size on this carb set, even one, can induce upper midrange stumbles under heavy or full throttle applications. If that occurs, you'll need to lean the needles a step by raising their clips one notch. Leaning the midrange will also affect the upper part of your idle or pilot circuit and may create a flat spot just off idle. If that happens, go up one size on the pilot jets (#27.5 stock to #30). Set your mix screws at about 2 1/4 turns out to start and fine tune from there. The mix screws will need to be re-set if you change pilot jets.
 
changed the plugs today and took her for a ride before the rain set in... she had all of her pep back. I will defineatly look into re-jetting the carbs this winter as well as a few other things to make this a little more dependable (ie fixing the electric start, new master on the front, and other little things that will make a big deal.. thanks again for all of your help...
 
Back
Top