XS1100 Backfire/slow throttle response

[amatco]

I recently purchased a XS1100 1981 Ventura. I am from North Dakota and this is my winter project.
The bike idles OK. When I try to increase the RPMs the engine hesitates, coughs and backfires. When the engine warms up the problem is not so noticable. The vacuum advance seems to be working properly. The timing plate on this model does not have slots in the housing to retard or advance the spark. I guess that is another problem . I do not how this model sets the timing? The service manual I have does does not show what I have mentioned. I have not checked the exhaust system. I have cleaned the carbs. I synct with a feeler guage. No mercury or vacuum test yet. Compression is good on all cylinders. I want to get this bike running as well as I can. I am a machinist and not a mechanic however I am learning.
If anyone has imput to share I would appreciate it.

Allen (amatco)

[skids]

It is running LEAN LEAN LEAN! It could be that the float level is set too shallow, The jets are restricted by gunk, the vacuum hole to operate the timing is clogged, or some other reason.

[amatco]

Adjusting Floats

Thanks for sharing the info --

I beleive your right. I am going to re-clean the carbs (maybe soak in a carb solution).
It appears that the only way I can richen the carbs is by very carefully bend the float arms. Are the specs in the manuals for proper float height reliable? If so, I will use them.

I admit when I clean the carbs I could have done a better job.
I did check for float height and they were all the same.

Thanks for the advice - I will let you know the results.

Have a good day, Allen

[crunchbird]

My experience is that the backfiring and hesitation can also mean a rich condition such as a leaking float valve, particularly around the O-ring on your 81 push-in seat, but then the backfire is steady at idle, too, so skids' lean call is probably right. My experience with lean was a loose manifold boot, the rubber/metal guys that hold the carb to the motor. The allenhead machine bolts were wiggling loose and the mounting surface needed spiffing up. It's easy to check. The rich backfire was a sporadic cannonshot, while the lean backfire was an annoying rapid light machinegun.

[sixtysix]

Your problem is the carbs, or a vac leak or some combination of the two. Carbs will never be cleaned right until you disassemble all the insides. Floats, needle valves and seats, emultion tubes(needle jet) and diphrams (with jet needle), and the air and pilot jets. Get the K+L kit with all the stuff in it and replace it all with new ($20 more or less each, check out recent threads on this).

As far as ignition goes the 81 was different than all the other models and had an electronic advance curve built into the CDI unit (black box).

Many good carb tips here, read them all! I never had a carb apart till a couple of years ago and used the people and info here to help me along. I am practically dangerous on carbs now . It's no rocket science but must be done correctly.

Good luck....BTW it's a Venturer not a Ventura

[nashville_bill]

Be careful when cleaning carbs that you don't dip them in carb cleaning solution because the throttle shafts have rubber seals inside and must be removed before using caustic solution.

[oldfart]

carb cleaning

Also,be very careful when cleaning that you do not lose the spring or o-ring or spring washer in the four mixture screws.(very small parts that you may not even know are there)been there done that,albeit 20 years ago....Will

[amatco]

I certainly appreciate all the contructive replys. It is nice to know I can lean on you guys for the expertise where otherwise I would be on my own. I am sure I will have other problems to solve with the bike but you know -- I sort of enjoy it!

Thanks much, Allen

[nashville_bill]

If you find that you do need the washers and o-rings, MikesXS has them for about $3. You can find him at http://www.serve.com/dlewis/mikesxs/mikesxsindex.html . He specializes in XS650 parts but there are a lot of parts that can be substituted for XS11 ones. He also has the rubber gasket that fits in the gas cap and keeps the gas from running all over your gas tank when it is very full. Check it out.

[amatco]

Main jets

I noticed that my carbs had #110 main jets installed. The book calls for 115/120 . I ordered #120 for all 4 carbs. I also noticed that cylinder No. 1 and 4 call for #115 main jets and cylinders 2 and 3 calls for #120 main jets. Why is this? If anyone knows let me know. Thanks

[Jerry]

The richer main jets for the 2 inner cylinders was thought to help them run a bit cooler. 1 and 4 are out in the air more than 2 and 3.

In real life it doesn't seem to make a lot of difference.

[skids]

Re: Adjusting Floats

Allen: I didn't catch your question until today. I don't know what float height spacs you are getting from the "manual." If you are using a Clymers, there is a supplement section for the newer bikes but be aware that there is nothing specified for the 81 models regarding setting the heights with the carbs upside-down. They suggest the U-tube method. Those carbs are identical to the 80 carbs however (go figure!)

Originally posted by amatco
Are the specs in the manuals for proper float height reliable? If so, I will use them Have a good day, Allen