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Vstar 1100 (2004) - Lean issues

110 Views 4 Replies 3 Participants Last post by  nick57
Hi everyone - I'm new to posting, but have been using the forums for all sorts of useful information for a while now. I have a 2004 V Star 1100 with slip-on exhaust that is giving me fits after I attempted to install a POD kit. The previous owner had a Kuryakyn air cleaner installed (skull design) where the plastic was cracking and falling apart, so I decided to just go the POD route instead, rather than replacing that with something else. The install was pretty straight-forward - I used a kit from the guy that hosts the facebook Vstar group, however I have not been able to get it running right since - it is showing lean at idle. Turning the PMS screws all the way in just makes it run better and increases the RPM, and unscrewing them reduces the RPM/Idle, which you can adjust back up with the idle screw, but backing it almost all the way out still shows lean symptoms. My understanding is that turning the PMS screw all the way in should kill the engine, as it would shut off all fuel flow to the carbs without the choke, but mine is not seeing this. This PMS screw response was seen whether operating both cylinders or pulling (and grounding) the plug boot on either cylinder.

I bought the extended Mikuni PMS screws that the Wiki mentions, so I know they are only supposed to be turned out about half of what the regular ones use, but, again, it doesn't seem to matter how far I turn them out - I'm still running lean. Specifically, at low throttle (before 1/2) the engine is extremely sluggish, surging, and there is popping and occasional backfiring in that range. Once I get past 1/2 throttle, everything starts to smooth out and the power difference is amazing, compared to what I had before. Applying a little choke seems to smooth out the lower end throttle response.

Carbs are perfectly balanced, but the vacuum level is low (around 150 mm/hg at 1000rpm) compared to the range indicated in the wiki (260-280). I had low compression on one of the cylinders, but that returned after readjusting the valves. I have replaced the intake boots and do not see an indication of any intake/exhaust leaking. Spraying starting fluid around the intake ports to the engine does not do anything. Spraying it around the carb intakes can sometimes see a response, but it is not consistent and I think it is overspray getting into the pod filters, since they are so close by. The carb intake/filter boots are in great shape, with no cracking evident.

The POD kit only changed the main jets (147.5) and added a washer to the needles. While in the Carb, I realized the seals and slide diaphragms could stand to be replaced, so I bought the Mikuni rebuild kit and went ahead and changed everything out, cleaned ports, etc. I also verified the float heights are good, per the Wiki recommendations. After experiencing the issue, I checked the pilot jet and found that the previous owner had changed it to 25, which seemed very high (17.5 or 20 are recommended). For sh--s and grins I popped a 20 in there, but it had no effect, so I went back to the 25.

I also did some research on the Kuryakn cleaner and found that the install instructions include a change to the air bleed port within the top slide chamber. I could not find any information about that port online, and I'm not sure if the kit made it bigger or smaller vs. stock. I have the stock ones coming from partzilla, just to eliminate that variable.

One interesting thing I saw last night when I was verifying the sync levels - I added a little choke to it. The RPM's went up, as expected, but the vacuum levels were what was weird - on the front cylinder, the vacuum levels rose significantly, but the rear cylinder maintained the same vacuum level. What would cause that?

Several people have indicated that I have an air leak somewhere, which is why I did all the other investigative work above, but I don't see any evidence of a leak anywhere. The fact that turning the PMS screws in doesn't kill the engine makes we wonder if there is an issue on the air cut-off circuit (that diaphragm was replaced and everything cleaned when I used the rebuild kit) or the choke/throttle advance (also serviced with the rebuild kit). Would an issue with either of those on just one carb (i.e. rear cylinder that did not increase vacuum under choke) create the same issue for both carbs, such that with only one cylinder running (either one), the PMS screw being all the way in would not kill the engine?

I've been at this for weeks (in between waiting for new parts to come in), and while it seems to be better than it originally was, it is nowhere near where it should be in the lower end throttle.

Sorry for the extremely long post, but I wanted to make sure I put as much information in here as I could, as you never know what might be relevant.
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go 17 or 20 on the pilot. the main is fine. do the pms screws have a white plastic knob or all brass. the white knob is 2 to 1 turns and the brass are 1 to 1.
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padell, Welcome from Sacramento, Ca. I noticed this is your first post if you post in New Member Introductions we could get to know you better.
go 17 or 20 on the pilot. the main is fine. do the pms screws have a white plastic knob or all brass. the white knob is 2 to 1 turns and the brass are 1 to 1.
Thanks for the response.

These are Mikuni brass pilot thumbscrews -from the wiki:
"Mikuni Pilot Thumbscrews:
These Mikuni parts will fit the 1100 carbs and allow the pilot to be adjusted without the use of tools... look for these Mikuni parts. NOTE: Set them accordingly (they are NOT the same as stock PMS screws!) Turn them out half as much as the stock screws.
(2) O-Ring, Fuel Screw N133.037
(2) Washer, Fuel Screw VM12/33
(2) Spring, Fuel Screw N133.206
(2) Screw, Pilot Fuel 604-26003"

These screws have a different profile from the stock screws, so I'm assuming that is why the turns are 1/2 of of stock.

But as noted above, the pilot screws don't help, regardless of where they are - the RPM and engine speed up all the way till they are fully seated. There is no "lean drop" at any point. It does seem to run a little better in the first half of the throttle with the screws 1 1/2 to 2 turns out, but that's relative - it's still horrible throttle response, with lots of stuttering, surging, and the occasional backfire.

As I also noted, I went back down to 20 on the pilot jet (from the 25 that was on it from the previous owner), but that did not improve things. Ultimately, since I'm running lean at the first half of the throttle (at least), going down in the pilot jet size doesn't seem like the right thing to help the lean condition.

I'm really thinking that the key to everything is figuring out why the vacuum is so low, compared to where it should be, and/or why the vacuum increased on only one of the carbs when applying the choke.... Any ideas on that part of the mystery?
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i am not an engine tuner but if the rpms go up when you turn the screws in it would suggest your to rich. I'd check the color of the plugs white would say lean. Where did you get the screws at, i didn't there available.
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