Running okay, but not great.

[Unkle Crusty]

Story so far. Bought an 83 XS400 with a well worn 6 speed DOHC motor. So bought another motor, 5 speed and put it in. Installed new front and rear wheel bearings, Installed new swing arm bearings and shaft. Removed the forward third of the air box.
And painted the main parts an ugly purple, that Mrs Snippets likes. Brakes work, tyres are good. New bars, old ones were bent.
Starts okay, sometimes on one. At WOT will not rev past 6K, back off throttle revs to 8K. No filters on carbs at moment, 125 main jets. When trying to go past 6K at WOT, getting a spluttering type sound. Might possibly be pre ignition, but I do not think so. Today checked compression, 163 pounds on both cylinders, so no worries there. Will check timing next, could not find much info here. Will study the ignition system on the 6 speed tomorrow. My current thinking is the main air jets are the wrong size. Carbs came off the 6 speed motor. I have the jet sizes for the XS400J and the XS400RJ, but not sure which is which. Have the jetting for GTI Dave. Paper style air filters going on in about two weeks. Later will put on foam type filters. Then will get serious about studying jet sizes. Meantime some pointers on ignition timing would help.
Also, carbs are clean, checked the float level.
Just insured Deep Purple for another year. This will be the winter bike. However as mentioned in another post, I have an XS11 if DP fails to proceed.
Forgot. Checked the plugs, they look good.

Unkle Crusty*

 

[xschris]

Without the proper air filters the bike will NOT run correctly. Get some foam filters and go from there

 

[16VGTIDave]

To even try to use the jetting I'm using, you have to have your bike setup like mine. UNI filters on stacks and HD Sportster mufflers would get you close enough that you could use my jetting as a starting point.

I wouldn't bother trying to get the jetting sorted until you have settled on the filters, mufflers, etc. you will end up chasing your tail...

 

[Unkle Crusty]

Thanks guys. I had heard they will not run well, with out the venturi effect of the stock setup. However it did not run well when it was stock.
Also forgot to mention, the mufflers are probably not stock.
This is my first encounter with these diaphragm carbs. Have them on the XS11, but all they needed was the needle to be lifted one notch. It runs real sweet.

I will pull the carbs and make a note of all the jets, and maybe get a few spares of different sizes. Have a main jet selection. Low end and mid range are fine.

I am on an Island, so have to plan ahead for trips to the big island, or the mainland.
Goods from the US go to Blaine WA and sit there until I pick them up.

Unkle Crusty*