A couple of problems

[jdblep]

Hi All,

Getting my 77 XS back together and have run into a few problems. First, the right-side is running a bit rough (the exhaust on that side is sporadic-strong puff/weak puff), and when revved puts out alot of white smoke. I have already adjusted the valves (.004, .006 warm), and checked compression (120psi on both cold). both plugs look pretty black. could this be a carb problem, or something more? Bike has pamco ignition, and seems to ride OK. I pulled the float bowls off, and the inside was clean (did shoot some carb cleaner down the passages). is there anything else i should be looking at?

 

[5twins]

Float setting, jet sizes, needle jet condition, needle clip setting.

 

[jdblep]

just an update, back from the garage. adjusting the idle mixture all the way in on the left side (good side) kills the engine. adjusting the idle mixture all the way in right-side (bad side), seems to make it run better. hope that this narrows it down. should i just buy a couple of rebuild kits, or are there specific parts for the carbs that i need?

 

[5twins]

The rebuild kits don't help much because the jet sizes included don't match what is in your carbs. If needed, all you might use from the kit is the gaskets and the float needle assembly. Sometimes it's cheaper just to buy those separately. If you go ahead and install all the rebuild kit parts, it can screw the carbs up worse than they already are because of the incorrect jet sizes.

Your right side carb appears to be running too rich. The mix screw turned in fully should kill it like on the left side. Turning the mix screw in leans the mix. It's still rich enough to run due to something else being off even with the screw turned all the way in. Check those items I mentioned in my 1st post.

 

[jdblep]

Thanks 5twins! looks like the carbs are coming off!

 

[gggGary]

looks like the carbs are coming off!

Now you've got it! Use the carb guide in the tech section print it out. NO short cuts, check off EVERY item and you should be good to go.

 

[littlebill31]

http://www.amckayltd.com/carbguide.pdf

 

[jdblep]

Well, pulled the carbs yesterday, and cleaned the hell out of them (carb cleaner and compressed air). Checked the jets for correct size, and condition, as well as the diaphragm. Everything looked OK. Put it back together, and no difference. Floats are correct (24mm), and all the passages seem to be clear. I decided to swap the needle and needle jet between the carbs, and that made no difference. Both sides are running rich, but the right side is much more so (this is the side where turning the idle mixture screw completely in has no effect). At this point i am stumped. Should i start ordering carb parts, find a different set (new or used), or try cleaning again?

Side note, PO had rear tire pressure around 80psi, i lowered that to around 45, and now the spokes make a ting when the wheel is rotated (is this a problem)?

Here is the bike (looks good, runs bad)

 

[5twins]

Did you verify that the needles are correct? Your carbs should have a 4M1 needle. Some of the rebuild kits come with a generic Y-22 needle. If these were installed in your carbs, they would be too rich. The Y-22 is about 5mm shorter than the 4M1. The only 650 carb sets it might possibly work in are the '70 -'73 ones.

You should also closely inspect the inside or bore on your needle jets. If the carbs had been all gummed up sometime in the past, that gas residue can actually eat away at the brass of the jets, making them larger and richer. Look for a grainy or sandpaper-like texture on the inside of the jet. That generally indicates it's been eaten away and damaged internally.

 

[jdblep]

Yes, the jets and needles are the correct part number. i didnt inspect the needle jet on the inside, perhaps i will just order new ones (with o-rings) and see what happens. Was thinking that the intake boots may be a problem as well. Not sure why when i switched the needles and needle jets between carbs the problem didnt follow. i am sure that after this is over i will owe 5twins a few beers!!!

 

[jdblep]

Well, just an update. Got new needles, needle jets, and intakes (with barbs) from Mikes this week. put them all on, and no change. getting pretty frustrated with this bike. If mikes had the 34mm kits in stock, i would have ordered one already, but alas they have been out for a while now. i also noticed that if i pull the cap off of the barb on the right side (bad side) it doesn't seem to make a difference (on left side it kills the bike). so my question is, do i look for another set of 38mm carbs, or any other parts that i should look at replacing? already cleaned the heck out of them (carb cleaner and compressed air), so i am fairly certain that their are no blocked passages. could it be something else besides the carbs?

 

[Classic]

Valves get adjusted when the engine is cold. Atleast 5hrs after a ride. Timing could be too retarded.

 

[jayel]

Side note, PO had rear tire pressure around 80psi, i lowered that to around 45, and now the spokes make a ting when the wheel is rotated (is this a problem)?

Here is the bike (looks good, runs bad)

80 is WAAAAY over 45 is still high what the recomended pressure on the side of the tires? yes check both front and rear (stock pressure back in the day was only 23-25psi front 28-30psi rear) but tires have changed and it's best to go with manufacters recomendation.... spokes "tinging" well it shouldn't do it from just rotating the wheel all spokes should be same general level of tightness and make the same ting when tapped (if you can tune a piano you can spoke a wheel) may just be settling back in after being over-inflated but if it doesn't calm down have it looked at by a real mechanic, I've seen a rear wheel collapse at speed and it wasn't pretty (hub failed) but spokes breaking would do the same

there are 3 small holes in the throat of the carb under the butterfly does carb cleaner come out of them from slow jet passage and air screw side (remove jet spray thru passage, remove air screw spary thru it)

 

[jdblep]

Yep, valves are dialed in, i have checked and rechecked them (3 times cold). I might see if i can borrow a timing light and check that next. The PO installed a pamco, so it should have been timed correctly then(?). last time i had the carbs completely apart (2 weeks ago) I did a thorough cleaning, and sprayed all the passages. cleaner did come out of each orifice, then used compressed air after that. all jets/passages looked clean. i am just wondering if instead of dropping all this $ on carb parts if it wouldn't be better to try a completely different set. i already have over $100 in the boots, needles, needle jets, gaskets and related.