'75 bogging when in gear and other issues

[ryanhall41]

My bike was running great one day and the next morning took a turn for the worse.

The Issue: When in gear I have very poor acceleration, to the point where I can get the bike fast enough to get past 2nd gear in most cases. If I try to go to a higher gear I start getting all kinds of vibrations down low. I can feel them most prominent in my foot controls area. Also when in neutral or clutch pulled in the throttle sounds very crisp and responsive but in gear I get kind of a "chuff chuff" sounds when trying to accelerate.

Remedies tried so far: To start are ground zero I emptied the tank and put fresh 93 octane in it and I seemed to get a little more acceleration but nothing that would slide me back in my seat like it used to. It's a 1975 xs650 so it did not come with vacuum barbs and it currently had keihin pwk 32's on it. I installed the carb boots from mike's with the new vacuum barbs and re-synced the carbs via the manometer method. Again I got a little more to the point where 1st and 2nd feel ok but still not like it used to. I still get a lot of vibrations past second that almost feel like some serious chain slap.

What's the next step here? The shop I took it to in order to do the wiring harness and some final button up didnt like to use loctite and I've had problems with bolts rattling loose, is there any in particular that I should check that may be causing these bogging issues.

Sorry, I'm new to the xs, any help would be great

 

[angus67]

Check spark, check advance, check pilots in the carbs.

 

[littlebill31]

Id also go through and do the basic adjustments.
In this order!!!!!
Cam chain tensioner, valve adjustments, timing and then carbs.

 

[retiredgentleman]

Those carbs have a very bad reputation. Try doing a search (upper right corner) for more information.
Stock mikuni carbs run great on these bikes.

 

[mrtwowheel]

Have you done a compression test? Your description is a lot like a bike running on one cylinder.

Scott

 

[ryanhall41]

Those carbs have a very bad reputation. Try doing a search (upper right corner) for more information.
Stock mikuni carbs run great on these bikes.

If all else fails I'll just boot these and go back to stock

Have you done a compression test? Your description is a lot like a bike running on one cylinder.

Scott

I've got good pressure coming out of both exhaust pipes so I dont believe that is the problem

 

[littlebill31]

I've got good pressure coming out of both exhaust pipes so I dont believe that is the problem

Ya, that doesn't mean anything. You need to physically check the compression in each cylinder with a gauge, not holding your hand behind a pipe.

 

[ryanhall41]

Ya, that doesn't mean anything. You need to physically check the compression in each cylinder with a gauge, not holding your hand behind a pipe.

Just shows what I know. This started as a summer project that got closer and closer to being a real bike and now I have to deal will actual mechanical problems vs just fabricating things that I think are cool.

When hooked up to the manometer the idle levels are deal on but when throttling they move slightly (say an inch of fluid height for each second of throttle) so I figured the compression was off between the 2 cylinders but close since I know the manometers are pretty sensitive. But again I could be completely missing the point here.

 

[littlebill31]

Compression is tested in the cylinders, not the carbs.
You remove the spark plugs, insert the compression gauge and kick/electric start the bike to cycle the engine (but not actually trying to start it). This shows the compression level built in each cylinder on the compression stroke. Low compression is not good. Could mean bad rings, valves not seating, hole in the piston.....

 

[mrtwowheel]

littlebill explained the reason for doing a compression test very well. A compression test is one of the first things to do when bringing a bike back to life.

 

[ryanhall41]

Update: Sure enough it was the left cylinder plug (I feel like a moron). Swapped it out and now it runs faster than ever especially since the carbs are actually synced instead of a guestimate.

Now I have to address the issue of why I have oil on my left plug (From the cylinder that wasnt running before)

 

[littlebill31]

Both of those plugs look like shit. They should not look like at all. Just a nice grayish clean color, not black.
Is it oil or is it running rich?
You really need to do a compression test. That will give you an idea if you have a problem. Then possible a leak down test.
Any idea if the engine has ever been rebuilt?

 

[retiredgentleman]

Oh yeah.................ugly plugs there for sure! I'd say if Ryan still has the original Mikuni carbs, he should put them back on the engine. The carbs he has now have been nothing but frustration for most who tried them. However, it may be that the head gasket is passing oil into the cylinders, and that means a top end re-build is needed. Yes, a compression test is a good idea, but compression can still measure in the normal range, with the head gasket passing oil.

 

[MaxPete]

All true - but the other thing is that those plugs may have been in there for a loooonnngggg time and so what you're seeing may just be the normal crud build up over a loooonnnngggg time.

I'd run it for a little while and THEN look at the plugs.

Pete

 

[weekendrider]

ryanhall you will want to read this thread.

 

[ryanhall41]

Thanks for them helps guys. Slowly chipping away at the problems as they arise.

The compression test yielded 145-150psi for the left cylinder and 150-155 for the right. I did each side 3 times with a warm engine.

The motor was bored out to 750 by the previous owner. It hasn't been apart in the 2 years I've owned it at least but I've only been able to put about 200 miles on it in the last few months since I just got it together

Here's another issues: 3rd gear, and only 3rd gear, seems to slip out of gear when under power. Now that I have Thebes's carbs synced nearly perfectly I can actually use it to climb to 4th but it still slips. Before I wouldn't just skip it all together because it skipped so badly. I founds another trans at a swap meet, just haven't gotten around to changing gears if that's actually my problem. It just doesn't make sense to me why carbs would yield any difference with this problem.