cylinder temps

[pahako]

Been working on a 79 special which is new to me. Other than a new fuse box, new plugs, carbs cleaned and float heights set, and carbs synced, I haven't done anything else yet. It seems to bog down sometimes when I give it a lot of throttle, and be lacking in power. I noticed that after riding cylinders 1 and 2 were much cooler than 3 and 4. I poured a little water on them and only got sizzle on 3 and 4. Should I check the mix screws, and if so, how many turns out would be close to a factory setting. As far as I know the bike is all stock, but have not checked the jet sizes.

Paul

[pahako]

Also found another issue that is quite possibly related. I remember reading somewhere on the forum that the vacum line should be connected to the carb body and not the manifold. I noticed on my bike, the line is connected to the manifold, and where it looks like it should be connected to the #2 carb, there is nothing there for it to connect to. The hole is there, but the brass fitting that should go in the hole is gone. Anyone no where I can get the brass tube for the hose to connect to? I'm sure this may have something to do with my problem, and will have to resync the carbs.

[motoman]

Also found another issue that is quite possibly related. I remember reading somewhere on the forum that the vacum line should be connected to the carb body and not the manifold. I noticed on my bike, the line is connected to the manifold, and where it looks like it should be connected to the #2 carb, there is nothing there for it to connect to. The hole is there, but the brass fitting that should go in the hole is gone. Anyone no where I can get the brass tube for the hose to connect to? I'm sure this may have something to do with my problem, and will have to resync the carbs.

Yup, need to get that hooked up to #2's ported vacuum. That basic vacuum leak U have on #2 WILL get you a holed piston.

The brass tube that goes in there has restictor built in(reduces size) so as to dampen vacuum pulses.
BTW, hooked where U have it, I'm surprised you don't here that advance can hammerin' to beat hell.

Sure someone will chime in as to where U can locate a proper tube to press in there.

[pahako]

I thought the advance seemed loud, but wasn't sure if that was normal for these bikes.

[Ken Talbot]

Been working on a 79 special which is new to me.....It seems to bog down sometimes when I give it a lot of throttle, and be lacking in power. I noticed that after riding cylinders 1 and 2 were much cooler than 3 and 4. I poured a little water on them and only got sizzle on 3 and 4.

The thing that cylinder #1 and #2 have in common is fuel supply. I'm guessing you are basically running only 2 cylinders so far. I would first check out the intricate plumbing diagram for the fuel system on Specials and see what is wrong there.

Leave the mixture screws alone for now, and temporarily plug the hole for the missing brass tube. You can make a makeshift metered orifice for the vacuum advance by drilling a very small hole in a piece of plastic and inserting that into the vacuum hose now connected to the manifold vacuum nipple.

Once you get fuel flowing to #1 and #2 and they come to life, you're going to think you have a whole new bike!

[motoman]

The thing that cylinder #1 and #2 have in common is fuel supply. I'm guessing you are basically running only 2 cylinders so far. I would first check out the intricate plumbing diagram for the fuel system on Specials and see what is wrong there.

Leave the mixture screws alone for now, and temporarily plug the hole for the missing brass tube. You can make a makeshift metered orifice for the vacuum advance by drilling a very small hole in a piece of plastic and inserting that into the vacuum hose now connected to the manifold vacuum nipple.

Once you get fuel flowing to #1 and #2 and they come to life, you're going to think you have a whole new bike!

.........could, but that would be counter productive. Ported vacuum is still what's needed, not manifold vacuum. In other words, it would have total advance when not wanted and no additional vacuum advance when needed.

[pahako]

I got it reversed on the original post. It was 1 and 2 that were hot and 3 and 4 that were cooler.
Should there just be a plug on the manifold on #2?
I'll check all the lines coming from the octi to see if they are correct. Mean while, if anyone has an old carb laying around and they can part with the brass tube let me know.

[pahako]

The line from the advance is connected to cylinder #1 barb. The line coming from the octy is connected to the #2 barb, but from what I understand, it should be connected to the barb on the #2 carb (which is missing), not the manifold. 3 and 4 barbs are capped. All other fuel lines are connected according to the diagram I have. Only the diagram I have shows the line coming from the advance going to the octy. Any thoughts?

[natemoen]

The octy should be connected to a carb boot like it is (it does not matter at all which carb boot it is connected too). The vacuum advance unit with you say is connected to #1 carb boot is what is supposed to be connected to the brass tube on the carb.

Take a pic of where the brass tube is supposed to be and post it. It is always possible that a previous owner replaced the #2 carb with a #4 carb (or even switched the two carbs around on the rack) and the hole is not even there.

[pahako]

The octy should be connected to a carb boot like it is (it does not matter at all which carb boot it is connected too). The vacuum advance unit with you say is connected to #1 carb boot is what is supposed to be connected to the brass tube on the carb.

Take a pic of where the brass tube is supposed to be and post it. It is always possible that a previous owner replaced the #2 carb with a #4 carb (or even switched the two carbs around on the rack) and the hole is not even there.

I haven't been able to figure out how to post a picture yet, but the #2 carb definitely has a hole for the tube and I can see the smaller hole in the bottom of it.
So I just need a tube for the carb, then run the hose to that, up from the advance?

[natemoen]

I haven't been able to figure out how to post a picture yet, but the #2 carb definitely has a hole for the tube and I can see the smaller hole in the bottom of it.
So I just need a tube for the carb, then run the hose to that, up from the advance?

Yes, that is correct.

[pahako]

OK, so I got the advance issue fixed, bike runs much better, and all cylinders get hot. Next issue is the revs don't come down as fast as they should when I blip the throttle. (the cable is moving freely) I resynced the carbs after I got the advance straightened out, and checked for air leaks with starting fluid. All good. So now I am thinking it is running to lean due to the mix screws. Only checked 1 and 4 due to the fact that I didn't feel like taking the gas tank off. #1 was only out 3/4 of a turn, and #4 was out only 1/4 of a turn. My question is; What is a good starting point for a 79 special, as far as how many turns out?

[natemoen]

Well first off, how did you fix the advance issue?

Second, a hanging idle is often caused by a lean mix. Where are your idle mix screws set at?

[pahako]

Well first off, how did you fix the advance issue?

Second, a hanging idle is often caused by a lean mix. Where are your idle mix screws set at?

I put a tube in the #2 carb where one had be missing, then connected the hose coming from the advance to it. The tube fit tight but I put a little jb weld around it to make sure it was sealed. (advance is muck quieter)

Are the idle mix screws the same as the "air and fuel" mix screws? the screws that I checked are called pilot screws in the diagram in my manual. I haven't checked 2 and 3 yet but. #1 was 3/4 of a turn out, and #4 was 1/4 of a turn out. I'll take the tank off later today and check 2 and 3.

[natemoen]

Yup, same screws. Start out at about 2.5 turns out from VERY LIGHTLY SEATED and then tune and sync from there.