81 xs400 with 400 maxim carbs

[dbou910]

This is my first post so bear with me. I picked up a 81 xs400 semi together with a box of parts as well. I noticed today while reviewing videos and this forum that I have a set a carbs from a xs400 maxim instead of the standard carbs I believe came with the bike. To back this theory up I started digging through the parts box only to find a few parts from what I believe to be the standard carb set. I have the bike running when choked with the maxim carbs that I have cleaned multiple times. My question is will these carbs work or do I need to pick up a different set?

Appears that its a 81 XS400SH

 

[willem]

welcome

To be honest, I can't think of a reason why you wouldn't be able to make the maxim carbs work. However, it will probably require some re-jetting and adjusting. Good thing is that you have the bike running already so you can work from there. Check your plugs and listen to the way your bike runs (high rising and unstable idle rpm, backfire and no power means you're running lean, bogging down, very low idle, and little power means you're running rich) and adjust the jets from there.

also don't forget to post some pics!

 

[willem]

actually, first rule out other factors that may be influencing your mixture: exhaust (manifold) leaks, valves out of spec, carbs out of sync, air/vacuum leaks at the carb boots or connections to air filter, the air filter itself, etc etc. If everything is 100% ok, and you still don't have a well-running bike, start changing out jets.

 

[bcware]

So you have an SOHC with DOHC carbs? I think that's what Drewpy did on his tracker, but it required some modification to get the carbs to fit.

Throw up some photos if you can so we can verify.

Here is the link just in case: http://www.xs400.com/forum/showthread.php?t=6406&highlight=tracker+jets+sorted

 

[dbou910]

I have order some new plugs today. I will post some more info and hopefully some pics after work. Thanks

 

[dbou910]

welcome

To be honest, I can't think of a reason why you wouldn't be able to make the maxim carbs work. However, it will probably require some re-jetting and adjusting. Good thing is that you have the bike running already so you can work from there. Check your plugs and listen to the way your bike runs (high rising and unstable idle rpm, backfire and no power means you're running lean, bogging down, very low idle, and little power means you're running rich) and adjust the jets from there.

also don't forget to post some pics!

Ok so I added new spark plugs. It seem to stabilize the rpm on the engine. I can even adjust the idle however I want but still only while choked.

heres what I will be checking next and correct me if im wrong.

1. float levels (while im at it I will try to identify the jets)
2. timing (because its easy to do)

Thanks for advice

 

[xschris]

You need some air filters to be able to tune it right

 

[dbou910]

You need some air filters to be able to tune it right

I have them they were just off at the time I took these. I was debating on pulling the carbs tonight but decide it could wait til tomorrow.

 

[bcware]

Do you actually have points?

Those carbs are definitely different than the ones on my 1978 SOHC.

 

[willem]

they don't look the same as my DOHC SECA though...

 

[xschris]

What kind of filters?

 

[dbou910]

What kind of filters?

They are the standard factory filters for the 81 xs400sh. They are a little hard to get on but they fit.

 

[xschris]

What are your idle mix screws set at and have you synced the carbs yet?

 

[16VGTIDave]

I agree with Willem, those carbs don't look like the ones on my Maxim either. Similar, but different. Mixed and matched parts from various years? Are the carb mounts installed upside down? Looks like the vacuum ports are facing down rather than up.

Have you checked for vacuum leaks?

 

[dbou910]

The carb mounts may be upside down. Im not sure. I did remove the to check for leaks but I mounted the back the way they were when I got the bike. I didnt check them manual....my bad. The carbs are a 3.5 turns out.

 

[dbou910]

And no I havent tried carb sync.

 

[dbou910]

float levels look good.

main jet:
135

pilots:
42.5

 

[willem]

I think they are off another type of bike. The carbs bodies don't look like the DOHC's, but the plastic floats do. I think Dave is maybe right, mix and match carbs?

do a valve clearance adjustment, put the carbs back on the right way (check the manual) after setting the float height, make sure there are no vacuum leaks, sync the carbs and adjust the idle mix, and report back

 

[xschris]

I would bump up to a 45 pilot and a 142.5 main and see how that goes. Also do a carb sync.

 

[Scorpio1963]

Those carbs in my opinion especialy with the jets size seem to match sohc b34`s maybe of a 79 or 80 model.
? is that fuel line hook up on the side of the carb body?