A little clarification please

[Denisesewa]

I've spent the past 3 weeks putting my basketcase together and getting it running decent as well as mocking everything up the way I want it before teardown and paint.
1977 , vm 34's , headers with Harley mufflers and pod air filters.
I have had some issues with timing, from everything I've read here so far I believe its just a tired engine.
The points plate ( NOS) is just about maxed out to get timing right. ( chain is adjusted properly)
When the cam comes to its TDC the Crank is 5 degrees past its TDC ( I believe this is cam chain stretch rather than a tooth off right? )
Dry compression is 120 and wet 140, both jugs are within 1 psi of each other ( electric start , mikuni VM34 carbs full open)
even so it does run rather well, time for a topend rebuild ?
jetting is another thing entirely , I'm @ 5500 feet , the carbs were jetted @ 180 mains , 42,5 pilots, it ran but crappy, I dropped the needle to leanest position and drilled some mains to 155, it runs rich still but closer, the thing thats confusing is the air screws are 1/4 turn out to get it to come off idle decently , I would think with that rich of a pilot at this altitude the air screw would be several turns out ? is this a function of the needle and needle jet being so rich ( and dropped to its leanest position) its screwing up the pilot circuit? ( I failed to note the needle and jet sizes)
I ordered 145 mains and 35 and 25 pilots but thinking the motor is so tired it may not be worth working on jetting until the top end is rebuilt? ( suggestions for needle and needle jet ? )
Anyway, any insight as to whether my thinking is correct and I'm on the right track would be appreciated.
Thanks

 

[TwoManyXS1Bs]

Welcome to the forum, Denisesewa.
Yeah, 5° retarded on the cam is a sign of a stretched camchain.
Mine's stretched 10°, but runs fine for me.
Yes, your jetting sounds much too rich for the "mile high".
On a BS carb, the air screw isn't an air screw. It simply allows more idle mix into the carb.
Have you downloaded the VM carb guide?
(2nd pdf in this link)

http://www.xs650.com/threads/carbs-carburetors.43/

 

[5twins]

The air screw is an air screw on VM carbs, not on stock BS vacuum carbs. A 42.5 pilot would be huge for the VM carbs. I've never heard of anybody running one that big in those carbs. The usual is low to mid 20's. You need to identify your needle and needle jet. There's a set recipe for the VMs when used on a 650 and the central point or foundation for that is the proper needle and needle jet. Then the main and pilot sizes are tailored around that.

 

[TwoManyXS1Bs]

VM!!! Thanx, 5twins. Edited above post...

 

[Denisesewa]

Thank you both for the input ( and link), I will find my needle and needle jet sizes this afternoon, as much as I've looked though I haven't found a reference for the correct sizes for this altitude so dont know what to order, there is a ton of info but sometimes it seems too much and gets over-whelming.
since both carbs are right side I am sure they have off the shelf jetting from sudco.

 

[TwoManyXS1Bs]

Just a guesstimation here.
Summertime, Denver, your density altitude will be around 76%-80%.
Apply the square root of that, maybe 0.86, to your jet sizes.
Ex: If recommend size is #140, times 0.86 gives #120 as corrected size...

 

[Denisesewa]

ok, so this is what I have-
needle is 6DH4 which is completely different taper profile than a 6F9 and appears to be richer overall.
needle jet is 159-P6 also richer than recommended P-5
slide is 2.5
the intake bell jet was still installed.
so being at 5500 ft should I just order the 6F9 and P-5 , remove the intake bell jet, call it close enough and jet the pilot and main around them?

 

[Denisesewa]

Just a guesstimation here.
Summertime, Denver, your density altitude will be around 76%-80%.
Apply the square root of that, maybe 0.86, to your jet sizes.
Ex: If recommend size is #140, times 0.86 gives #120 as corrected size...

Ah, thanks for that , so I am in the ballpark with a 155 main since recommended is 180, good to know, looks like I'll need #20 pilots.
So does this apply to needle and needle jet as well? ( see above post)

 

[5twins]

I think I'd stick with the 6F9 needle. I think the recommended needle jet is a P-4, 5, or 6? Maybe go with the leaner 4 on that? Yes, then jet the main and pilot around them.

Your small air screw setting doesn't seem to be giving the normal reaction. Like you said, with your large pilot you would expect to need several turns out. Maybe your other jetting is so far off that the screw is having little to no effect? Usually you can judge the correctness of your pilot jet choice by the air screw setting required. I think the range Mikuni likes to see is 3/4 to 1.5 turns out. Above or below that usually means your pilot jet is too large or too small. But remember, the air screw is for fine tuning. If your jetting is way off, it probably won't help or do much.

 

[mrtwowheel]

Basket case, just got it running........don't judge your compression numbers just yet. They are at the low side but they are even. After this engine runs for a while longer those numbers WILL go up.

Scott

 

[Denisesewa]

Thank you all for the helpful responses ( and to those who have posted such helpful info on this forum), very much appreciated !
I have ordered appropriate jets.
as for compression, I have run 4 tanks of fuel through the bike so far and compression hasn't really changed, it is running pretty good considering and the more I ride it the more I'm liking it, I definitely don't mind investing in it.

 

[mrtwowheel]

A half can of Seafoam to a tank of gas will clean out some carbon on the valves, seats, and free up the rings. Betcha that will raise the compression.

Scott

 

[Denisesewa]

Seafoam treatment is underway, it'll be interesting to see the results.