What am I missing?

[hotrdd]

Posted this in another thread but haven't had any replies. After going through the carbs and doing the cam chain tensioner, valves and timing the bike seems to be running worse. I feel like I have went through the engine and looked at everything but I'm sure I'm missing something. I am going to go back through the valves again since I only had a .005"and .008"feeler gauge when I did the intakes. This means the intakes could be anywhere between .005"and .007". I also took my single air intake off to make sure it wasn't playing into the equation. What would you be checking next?

1) Fixed the carb issues with the needles being in different spots and a missing diaphragm return spring.
2) Took the air cleaners off in case they were causing issues with the carb. Sync. (So the carbs are running without a filter)
3) Set the cam chain tension adjuster as per the website.
4) Went through and adjusted the valves.
5) Moved the Main jets up one size on both carbs.
6) Set both mix screws to 1.5 turns out.
7) Warmed the bike up.
8) Synced the carbs at idle (But as the RPM's climb the right carb has about 10"of more vacuum on my ATF manometer)

The bike is still on the stand but it seems to be running even rougher. As the RPM's go up I'm getting rapid popping from the exhaust but it's not very loud. The bike also seems to be shaking more now than it did before and making more engine noise.

What am I missing?

 

[650Skull]

A new thread because you weren't answered since yesterday............you have had a lot of help................get a manual

 

[hotrdd]

Sorry, I'll try to be more sensitive next time. I didn't realize this would upset someone. I was very open that this was posted in another thread.

I'm sure I'm missing something stupid because I have read everything dozens of times and keep a manual and a note book with all hard copies of the carb. Guide beside the bike. I have also scoured the tech section and watched all of the video's. I'll go back to square one and do it all over again. I can honestly say that I don't know what I'm missing.

 

[gggGary]

What's the compression like?
Did you try spraying carb cleaner around the intakes looking for leaks?
Still have vacuum petcocks?

 

[hotrdd]

Thanks gggGary

- Just checked compression and it's 125 on each side.

- I had some old carb cleaner around and spraying it on the carb boots and seals but it made no difference to the RPM, I'll try and get a new can of it tomorrow and try that as well.

- I have manual petcocks.

I went through the cam adjustment, valves and timing again tonight and then synched the carbs at idle. One issue I did see though is that the left carb. started leaking out of the small little pipe at the bottom of the carb. This is while the bike was running, as soon as I turned off the gas it stopped. I turned the gas back on and everything was fine again.

 

[hotrdd]

I'm reading through the carb guide again tonight.

 

[Dead Boy]

The carb leak is probably misadjusted float height.

 

[hotrdd]

Would the leak be that sporadic and then just fix itself? I did adjust the floats during the carb rebuild but at this point anything is under consideration.

 

[gggGary]

Crap from the gas tank getting on the float valve seat would be a good guess. Like XSLeo says; washer seals the BS38's

 

[GreasyC]

Did you remember to hold the throttle open during your compression test? 125 is low, but not impossible.

 

[hotrdd]

I used a complete rebuild kit but don't specifically remember an oring for the float. I'll need to check if the 76 BS38's had one. Could a bad float be causing my other issues with rough running and unable to sync when the RPMs increase?

 

[XSive3X]

what pipes are you running with the vacume barbs?

 

[hotrdd]

XSive3X - not sure I understand the question. I have the regular headers on the bike that expand to a 2 1/2" pipe with baffles. Both are the same length.

 

[XSLeo]

Carb sync with the manometer is for idle only. You get sporadic readings at anything over idle.
The pipe on the bottom of the float bowl is the bowl over flow. Fuel comes out the over flow anytime there is too much fuel in the bowl. intermittent over flow usually means crap coming from the tank holds the float valve open, then gets knocked out then seals fine untill the next piece of crap come by. Fuel filters between the tank and carbs help.
On the 76 carbs the float valves scrw in and seal with a washer. All the BS38 carbs did, the BS34 carbs the valve is pressed inplace, sealed with an o-ring, held in with a clip and screw.
Leo

 

[gggGary]

Correction that All the BS38s used a threaded float valve body. When you have the carbs apart, dip the floats in a cup of hot water; bubbles = junk.

 

[hotrdd]

I have fuel filters on both lines heading to the carbs. If I just see intermittent fuel leakage should I still consider taking the carbs off and re-checking the float height?

Here are some other items that I plan at looking at tonight. Mains are currently 132.5 with the needle moved down on position.

1) Switch the manometer Tube sides to see if there is a difference? (Maybe one of the tubes is bad or has an air leak) Sounds like things won’t change though.
2) Put in new spark plugs. How can you tell when one is fouled?
3) Test the diaphragms again and make sure they drop properly.
4) Spray carb. Cleaner on the seal and boots and monitor the RPM for change.
5) Pull the carbs and check float heights (25 mm +/- 1mm)

 

[GreasyC]

6) ride it?

Hard to say a lot about it from running it on the stand for a couple minutes. These bikes shake like hell and make a ton of engine noise (the lack of a water jacket over the engine means you hear every little noise from inside) so those "symptoms" don't necessarily mean anything. When you stand next to an idling XS you can feel the vibrations in the ground through your boots. The front end doesn't usually pogo right off the ground but it looks like it wants to. So what's left, you're getting some popping on the right exhaust? Check for leaks in the intake and exhaust tracts, but you can't choose jets and tune the carbs without riding it.

 

[hotrdd]

Did steps 1-4 and then 6 and everything seemed to be better but after about 3 miles I pulled over and fuel was leaking out of the right carb over flow. I turned off both petcocks for a minute and then turned them back on and everything was fine again. The reason I stopped was because it started to run rough and I think the overflow from the bowl was choking things. I'm going to do some digging and see if it's possible to check the float height while the carbs are still mounted. Otherwise they'll be coming off.

Thanks to GreasyC for suggesting #6 it got my spirits back up. And now it's time for a drink.

 

[GreasyC]

It's annoying and messy when they overflow but you'll have that fixed pretty easy. There is a method to check the fuel height while the carbs are on, you should be able to find threads about it here. Involves getting a spare set of drain plugs for the bottoms of the bowls and drilling a hole in them to connect to a plastic sight tube so you can "read" the fuel level like you would on a master cylinder reservoir. Honestly it always seemed like more trouble than you really need to go to so I've never tried it.

I'd take them off and go over the float valves and their seats with cleaner and a brush. I try to shoot cleaner into the valve by pressing it open over and over while shooting it. No idea if it works or is just voodoo but it doesn't hurt anyways. Try to make sure the washers under the valve seats were replaced in their original direction. The seats should have worn a ring in one side of the washer and you want that face up to stay matched up with the seat. Check the floats for leaks as suggested above. Then personally I'd set the floats a mm or two higher than you had them before for good measure. Measure and adjust both sides of each float. Make sure they're straight up and down and square to the bowl because they do get cock eyed and bind up sometimes. Don't hold the carb in your hand and tip it every which way as you screw the bowl back on because that also seems to encourage them to get cock eyed and stuck in my experience. Leave the carb straight up and down on the table until you have the bowl screwed on.

 

[XSLeo]

When the float valves stick open so fuel runs out the over flow makes it run very rich on that side.
If you pull the carbs pull the float valve needle out, take a Q-tip, pull off the cotton off on end, wrap the end with a small amount of 0000 steel wool. use this steel Q-tip to clean the seat of the valve.
This removes all the built up crud on the seat and any small burrs that maybe there.
This is a tip from XSJohn.
Leo