XS650 Mikuni VM34 Carb Kit - Which one to buy?

I purchased the 34102 VM34 mm Carb Kit #1 from Hoos Racing, installed them and fired them up the other day. The bike started up after a few tries and the carbs sound great. The set included manifolds with threaded holes for barbs.

Can someone tell me what size barbs in need for testing with a manometer? I'd determine the hole size myself but the bike is at DIY shop and I want to pick up the barbs before I head back to work on the bike again.
 
I've been doing a lot of swapping of main jets and needle positions and have a couple questions. I'm read, re-read, practically memorized the Amckayltd and Sudco Tuning manuals , which has been very helpful, but since this is my first and only bike I need to ask specific questions. Since I have no previous experience with motors, cars, bikes, etc. I can't tell from performance if the bike is running rich or lean.

For example the Sudco manual states "Typical Lean Mixture Symptoms: Engine acceleration is flat or slow to pick up." and Typical Rich Mixture Symptoms: Engine acceleration is flat, uneven, not crisp." Pretty much reads like the same thing to me!

Here are the specs:

1980 XS650SG
Stock engine
Compression even around 130-140 if memory serves me correctly
Stock exhaust and muffler - had leaks but are now blocked with JB Weld High Heat
Pamco (real one) ignition with e-advance
PMA - 13 to 14 volts
Can chain tension set
Valve spacing set
Timing set
VM34 Carbs from Hoos Racing
K&N style rad 5" pleated air filters
Slides - installed with cutaway at rear - adjusted with drill bits/monometer - adjusted to pull together
Needle Jet - not confirmed but 159 series, P5 or P6
Needle - 6F9 (swapped from 6DP1 that came with the kit) - clip in 3 slot
Pilot jets - VM22/210 series, size 25
Mixture screw - 3/4 turns out
Main Jet - 180

Idle to 1/2 throttle feels good.

I had the needle clip at the 2nd slot for a while and tried mains from 175 to 200 in intervals of 5. The only real difference I noticed was a bit of sluggishness and backfiring from 3/4 to full throttle with the 175. I could not notice a difference in performance from 180 to 200 and no backfiring. There was slight sluggishness from 1/2 to 3/4 throttle.

Needle clip is now at 3rd slot and seems slighly better from 1/2 to 3/4.

In second, third or fourth gear the bike is sluggish on acceleration from 1/2 to WOT while at 3,000 rpms. In fifth gear it responds better.

At all of the above settings plugs are carbon fouled.

Is this to be expected? Should I not expect the same performance in lower gears that I am getting in fifth?
 
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Peter something doesn't sound right, I never sell with a 6dh4 ( unless those got away from me before i jetted. if they came with a 6Dh4 then they probably have a big 159-Q2 for needle jet, which is to big. Email me at gary@hoosracing.com and we will get this sorted out. You will need to check the needle jet. Gary
 
No, Peter, what you're experiencing is not normal. Guys don't want to hear this and usually disregard the advice, so I'll offer it to you once only and expect you to do your own search, because everything you need to know has already been addressed in other posts: Troubleshoot your ignition. Especially, make sure that you do not have a big (>0.4V) voltage drop between your battery and igniter box and between battery and ignition coil.
 
I got mine from 650 Central and they worked great out of the box with my 700cc Shell #1 cam.
 
Thanks Grizld. I will take those readings.

OHRider. I don’t put any blame on the carbs I received from Gary Hoos or his service. I believe my lack of experience is the only reason my bike is not performing perfectly.
 
Did some ignition testing.
Coil:
Came with XSCharge's PMA kit. It is Part #17-6822 from XS650direct.com. See attachment.
Between primaries is 5.7 ohms. Spec states 4.5 ohms. Is this significant enough to cause choppiness at 3/4 to WOT?
Between secondaries is 16,500 ohms.
Open between primes and secondaries.

Also noticed, what I took to be, corrosion around the the Pamco E-advance chip MSP430G2331. There is also a silver ring on the top of the chip that isn't usually on chips.
IMG_0967.jpg
I wouldn't think the chip would be "partially" blown but I could be wrong. Ordered some from Mouser.

Voltage between power (forgot to mention the bike has an M-Unit) and coil is 12.46 V.
Between power and Pamco igniter box is 12.08 V
Difference of 0.38 V. Just less than the 0.4V max difference Grizld mentioned.

My questions are:
Is the resistance of 5.7 ohms between the coil's primaries an issue? I've only read that low or no resistance between primaries is an issue.
Could the chip possibly be an issue? The Pamco unit certainly works - Idle to 3/4 throttle runs good.
 

Attachments

  • coil spec.pdf
    327.3 KB · Views: 181
Turn on the keyswitch, check battery voltage, then check voltage at coil and box. A drop of .038V on one wire in the system would be something I'd want to eliminate. Resistance at a bad connection creates heat and heat causes more resistance, so you could be looking at less than 12.08V under running conditions.
 
Grizld.

Remeasured.
Battery is 13.12V
The M-Unit takes battery/PMA power and regulates it so the output terminal that feeds the coil and Pamco is 12.13V.
Coil is also 12.13V.
Pamco Igniter box is 12.08V.
0.05V drop between power and igniter box.

Does the coil primary resistance of 5.7 ohm seem right?
 
Thanks Grizld. I will take those readings.

OHRider. I don’t put any blame on the carbs I received from Gary Hoos or his service. I believe my lack of experience is the only reason my bike is not performing perfectly.
I was just saying I got my carbs from 650 Central. Did not even know about Gary until 650 Central told me about him. I got my pistons and cam from Gary.
 
Grizld. Does the coil primary resistance of 5.7 ohm seem right?

IIRC recommended is 2.4 to 3.0 ohms Guess I would thinking about getting a coil in that range. Accel 140403 coils have been working well for me.
 
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Peter, I don't know the coil requirements for Pamco ignitions, listen to gggGary on that. Sounds like you have no power supply issues (apart from a battery that may need to be topped up). +1 re. Accel coils--not cheap, but worth every penny of the price. When you get the ignition straightened out we'll get back to the carbies, no point playing with them before that. Last question: what elevation are you riding at?
 
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I’m in Toronto. About 250 ft / 76 M above sea level.

Pamco recommends the coil I have but states ranges in different documents as 2 to 3 and 2.5 to 4.5. The spec on Mikesxs/xs650direct is 4.5. Mine is 5.7.
 
OK, altitude isn't part of the problem. If your reading is accurate, you know that the primary resistance of your coil is out of range for your ignition in spite of the nominal rating for the coil; not surprising (to me, anyway) for the Chiwanese stuff from Mike's XS. The rated primary resistance of the Accel 140403 coil that gggGary recommended is 3 ohms.
 
Well. Since I last posted I've learned a thing or two about ignition coils...and multi-meters. Turns out you need to see how much resistance there is between the black prong and the red prong and subtract that from the reading of the item you are measuring. Oops!

My coil is within the spec range needed for the Pamco ignition unit - 4.2 ohms primary resistance.

Going to recheck the float heights then back to jetting and needle positions...and plug chops eventually.

Picked up a couple of, what now are back up, coils before I found out about the multi-meter trick.
 
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When you check float level, be sure you're measuring the height of the actuator blades ("fork tines") at the point where the horizontal float pins make contact. But before you alter the float adjustment, you might want to get a spare float bowl plug, tap it for a hose barb, and attach a piece of clear hose to check fuel level directly. (A tip from gggGary's bag of tricks: get a 6x1.0 mm. grease zerk from Big Box Auto Parts, drill it to remove ball and spring, and use it for a hose barb).

Edit: Don't know what meter you're using, but 1.5 ohm resistance between the probes is a lot. Cheap meters don't tend to do a very good job on low resistance measurements.
 
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