Cold No. 1 Cylinder

[BigOates]

First off thanks to this site I've finally got the bike back together and running. I bought this as a project back in March. Discovered the bottoms end was shot and lucked out to get a cheap parts bike.

First off I'm using an 80 special case, advances, and tic box with the good 81 top end. I'm running the K&N pods, dynajet stage 3 kit, and a four into one exhaust. I fired her up for a short ride the other day got back and realized the no. One cylinder is cold. I spent the other day trying to track down the problem and would like some advice as to where to look.

I confirmed the vacuum advance is working. The tci box is good. Mechanical advance wires are good. I also tried a different set of coils with no change. Swapping plugs and/or wires and caps make no difference. Good spark was confirmed with the colortune and also by grounding to the block. Compression was good in all four cylinders. I had previously cleaned all the carburetors and did again that day. I noticed the pilot jet was stripped in the carb body. I swapped everything over to a spare carb body I had and same problem. The carbs were all vacuum synced. Floats set at 23mm. Confirmed fuel filling the bowl with the drain and tubing method. Ive adjust the mixture screws on 2-4 with the color tune and get a great blue with a hint of yellow combustion. Nothing but the spark on 1. Before I decided to call it a night I took off the pod filter on one while it was running. When I put my hand over the throat I felt some fuel come up through the carb. There was a strong yellow combustion showing on the color tune then for a bit then back to just the spark.

I'm assuming that this points to the carb as the problem? Pilot jet circuit maybe? When I pulled the pilot jet out and let it soak in cleaner it seemed to be clean. It's got the six holes in the side and the tip appears to be solid.

Any help would be greatly appreciated as I'm supposed to be taking this baby on a road trip in two weeks and would much rather be on this for a long ride than my lil magna!

[WMarshy]

Hey Oats, nice detail in your writeup. Sounds like you already checked most of the low hanging fruit. I'd check compression across all 4 cylinders (throttle wide open). Any idea what your valve lash is? Might consider checking it if the compression is low in that cylinder...

[Courtney]

Bizarre. Have you tried putting a 1/2 tsp of gas in cylinder 1 and firing it up and really revving it up to see if it sucks whatever is blocking it out of the carb. I know it sounds silly, but I saw my buddy Syd do this once and the carb started to work fine??? Seems as if the revs created enough suction with that cylinder firing to clear whatever it was. Certainly easy to try.

[DGXSER]

Try pulling the pod filter off no 1 and spraying in some carb cleaner or starting fluid.

As you said, it is carb related. Now, look at the plug after it has not been firing. See if the plug is wet with fuel (to much fuel), or dry as a bone, not enough fuel. If the plug is dry, it would appear you have another trip into the carbs in store. I recently cleaned a set soaking them in pine sol mixed about 50/50 with water. Smelled bad, but boy did it clean the stuff out of them!

[WMarshy]

... Ive adjust the mixture screws on 2-4 with the color tune and get a great blue with a hint of yellow combustion. Nothing but the spark on 1. Before I decided to call it a night I took off the pod filter on one while it was running. When I put my hand over the throat I felt some fuel come up through the carb. There was a strong yellow combustion showing on the color tune then for a bit then back to just the spark.
...

Intermittent fuel supply issue. Might have a kinked fuel line? If so, both carbs in that bank would have the same problem (common supply). Did you happen to notice any issue with the neighbor carb?

The new carb body you put on is the same style? Maybe blocked bowl vent?

[TopCatGr58]

Hey Oates,

Got compression, got spark, but only spark in colortune means no fuel.

Replaced with new carb body....cleaned pilot JET, but did you actually clean the PILOT CIRCUIT with spray carb cleaner ensuring that it flows THRU the entire circuit? Also, pilot jet screw....if 79 carbs..tip broken off in carb body?

However, when riding....mains should have kicked in at higher rpms so exhaust should have been warm...perhaps not sizzling but not cold!

SO.....you say vacuum synched....but symptoms do point possibly to vac leak? Where did spare carb body come from? Could have butterfly shaft seals leaks?? Hand held over carb inlet got spritzed with fuel, but there may not be enough vac. when inlet bell open to actually be able to suck fuel up from the bowl?? Folks have found leaks where intake boots meet engine head. Also, synch port caps can harden/crack and leak.

Fuel supply issue...verify that the fuel "T" isn't blocked on the offending carb side...they can get junk built up inside of them...could be open just on the #2 carb side..you may need to separate the carb body from the rack...but maybe not...just would need to pull the float bowl...and float needle seat, then spray carb cleaner into fuel "T" to see if it comes thru to carb?

Good luck.
T.C.

[Yard Dogg]

You should blow out all the ports with compressed air. Also, would hurt to make sue the emulsion tubes are clean. A lot of people skip it cause they don't know they are removable. Could also be a leaky vacuum diaphragm.

[BigOates]

I'm definitely leaning towards the carbs now. I came home from work this morning and pulled the valve covers. All valve lash is within the tolerable limits. Compression on all cylinders was 115-120 on an almost dead battery (it's charging now so can recheck if need be). I did notice when I pulled the plugs that there is some carbon build up on the top of the no. 1 piston. The others are still as squeaky clean as they were when I polished them.

I have the later model carbs on the bike and the po had a ton of spare parts from another rack of late model carbs. I'm pretty sure the fuel t isn't blocked as the float bowl fills completely and is within spec using the tubing.

If the same problem with this carb body is the same as the last, I would assume the problem would lie with one of the parts I swapped over (float need valve and seat, float, jets, diaphragm, and spring? Or a vacuum leak.

I'm about to go pull them while the battery is charging and double check the fuel t is clear. And recheck the pilot circuit is clear and clean them one more time. I didn't think to check the intake boots. I've got a few spares that came with the other set of carbs If I need to swap. I assume I'm looking for tightness of the screws and checking the boot for cracks?

Thanks a ton for the help thus far. At least I feel like we're narrowing the problem down one system at a time! I'll report back once I get the battery charged.

[3Phase]

BigOates,

You'll see spark-only in the Colortune when the mixture doesn't ignite -- rich or lean.

If you're seeing consistent spark but an intermittent yellow in the Colortune (rich) and carbon building up on the #1 piston you've most likely got too much fuel going to the #1 cylinder.

From your description it seems like the cylinder is flooding until the fuel level can drop enough for the mixture to become lean enough to ignite... sort of. The float valve then opens up and refills the float bowl and the mixture goes rich again. Lather. Rinse. Repeat.

Hook up that Colortune and use a clear plastic tube from the #1 float bowl drain to double check the dynamic fuel level (float height setting) when the engine is running. Watch the Colortune while tapping on the #1 float bowl with small block of wood or a rawhide mallet and see if that changes anything.


You can also check:

The float bowl gasket. Make sure the floats are not getting hung up on the gasket and trim it if necessary.

The fuel jets. Make sure the main and low speed fuel jets aren't loose, cracked, broken, or sitting in the bottom of the float bowl.

Make sure the carburetor slide is working.

Check the float bowl vent circuit and make sure it's not plugged.



Yeah, I know, I hate pulling the airbox and messing with carburetors too!

[BigOates]

Well fellas I finally figured it out. Did as everyone suggested and cleaned them. Took off the carb boot and realized it wasn't sealed with permatex or a gasket (been fixing the po's "rebuild" since I bought this damned thing!). So I sealed it up and reassembled the carbs. Still nothing. I then took 3phase's advice and started tapping on the bowl. It started firing irregularly, but I was getting a blue flame. Took them back off and saw the float bowl gasket was binding the float. Trimmed the gasket and reassembled. Still firing intermittently, but I was finally making progress. I then got the bright idea to loosen the enricher circuit so i could just enrich the no. 1 carb. What did ya know! Great yellow flame. Took the, apart for the bajillionth time and decided to really compare and swap the jets on one and four... Now I realized my stupid mistake.... The no. 1 carb had the six hole 42.5 pilot jet.... All the others have the no hole 47.5 jets. Swapped the jets around and the problem moved to 4.

Not gonna say how long I've spent trying to figure this out.... Well who cares, at least 12-15 hours tracking down dead ends. On the bright side, my carbs are so clean you could eat out of them, the float issue was eventually going to be a problem, and so was the unsealed carb boot.

I new I had the late model carbs, but apparently they're off an XJ due to the pilot jets and my spare rack must be abastardized late model set...

Now where can I get a no holed 47.5 pilot jet from? I'll be overnighting it when I find one cause I'm ready to ride!

Thanks a ton for all the help as well. This forum and the members here are great!

[3Phase]

BigOats,

Congratulations! You didn't make a stupid mistake but like way too many of us here: "You have been P.O.d!" The t-shirt rack is over there by the counter and the free coffee and donuts is first come; first serve.


PJ Motorsports sells individual jets for $7.95 each:-
Mikuni N151.067 Pilot Jet

If you have a motorcycle dealership nearby just go to their parts department with the jet you need in your hand! and buy one. They should have a box of Genuine Mikuni jets and they are not expensive. Make sure you get a Mikuni jet. If they cop an attitude or want $50 or something to dig out the tray of jets, just smile and wave but at least try to give a local shop a chance.

There's nothing wrong with jets made by other manufacturers but the numbers and hole sizes don't always match up with one another and it can be a pain in the you-know-what to try to tune one carburetor out of four using one jet from a different manufacturer even if the cross-reference chart says it'll work.

However you decide to go, make sure you synchronize the carburetors. There are entire threads devoted to that subject and it can take on an almost religious fervor. Here's a link to a YouTube video I made a while back for my '80G:-

XS1100 Carb Sync

Happy tuning!

--

[GLoweVA]

..... It's got the six holes in the side and the tip appears to be solid.....

Sorry I didn't read this sooner, but in your initial post, you had the answer right there.
That pilot jet needs a hole in the tip.

[GLoweVA]

If you had a leak at the carb boot, you wouldn't have been able to vac sync it.

[BigOates]

Sorry I didn't read this sooner, but in your initial post, you had the answer right there.
That pilot jet needs a hole in the tip.

Well on the bright side I was about ten minutes away from pulling the heads to make sure I didn't drop a valve. At least I avoided that again! My jet should be in today or tomorrow. Hopefully have her running and put some miles on her before the road trip on the 22nd.