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Discussion Starter #1
Here’s the scenario:
back block plugs in my opinion look great
289144


front block plugs look mega lean!
289145


idle sounds good, no skipping. Removed plugs to check compression, all four blowing fine. I have new carb boots, I have new carb boot clamps, carb went through the ultrasonic wash a month ago. Have checked for leaks with a torch.

another issue is that mega lean front block is spitting liquid:
289146


these are brand new plugs and these results with the plugs are moving at 1/4 throttle in first gear for 2 minutes straight.

what do you think the issue could be? Ignition coil? I took the plugs out too and tested the spark on the engine too and all seemed fine.

Thoughts? Im
 

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I’d go ride it for a half hour or so then reevaluate. 2 minutes of idling doesn’t tell you much.


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Discussion Starter #3
I’d go ride it for a half hour or so then reevaluate. 2 minutes of idling doesn’t tell you much.


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I was thinking about that. I got a dynojet needle and am in the middle of tuning it. I warmed up the bike for 10 mins and then did 1/8 throttle for 2 mins pulled the plugs. 1/4 throttle 2 mins then pulled the plugs and the above photos are the results.

here’s a photo of all the plugs after 40miles but the clip position was one richer than it is now.
289148

the bottom two are the front block
 

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2000 Honda Shadow Spirit VT1100C
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3,144 Posts
Here’s the scenario:
back block plugs in my opinion look great
View attachment 289144

front block plugs look mega lean!
View attachment 289145

idle sounds good, no skipping. Removed plugs to check compression, all four blowing fine. I have new carb boots, I have new carb boot clamps, carb went through the ultrasonic wash a month ago. Have checked for leaks with a torch.

another issue is that mega lean front block is spitting liquid:
View attachment 289146

these are brand new plugs and these results with the plugs are moving at 1/4 throttle in first gear for 2 minutes straight.

what do you think the issue could be? Ignition coil? I took the plugs out too and tested the spark on the engine too and all seemed fine.

Thoughts? Im
How did the bike run before you decided to fix it by rejetting it?
 

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2001 Valkyrie I/S
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It looks like to me that the first plug is dark and sooty which would mean it's running rich. The other plug might be a little lean but not much.
 

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Discussion Starter #8
How did the bike run before you decided to fix it by rejetting it?
It was black black rich and would need to change plugs every 60-70km. That’s when it was 42 pilot , 45 main and stock needle with 2 shins. Got the dyno needle and it’s been a challenge with the super tapered needle. I’ve found that 35 pilot and 40 main have been a sweet spot so far
 

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1999 Shadow 750 ACE VT750CD3 Modified
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Can't you even get it running at a fair speed and nurse it up to full throttle?
Then look at the plugs.
Getting full throttle right is the first and most critical thing.
 

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Discussion Starter #12
Can't you even get it running at a fair speed and nurse it up to full throttle?
Then look at the plugs.
Getting full throttle right is the first and most critical thing.
I could do that. I just figured In tuning the bike i was suppose to start with pilots a work my way up.
I set the AF and idle nicely. Then moved on to1/8 throttle, then 1/4 and my next step was going to be 1/2 then wot but I stopped at 1/4 cause of this issue. I didn’t think it made sense to keep going when one block isn’t working properly
 

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1999 Shadow 750 ACE VT750CD3 Modified
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No, Main jets effect everything except the idle circuit so work backwards from that.
Go here and follow the proceedure for "Low RPM Engines" and you will be working in the right direction.
At some point you will probably end up with different size main jets front to back to make the plugs look right, but you have to get there first.
 

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Discussion Starter #14
No, Main jets effect everything except the idle circuit so work backwards from that.
Go here and follow the proceedure for "Low RPM Engines" and you will be working in the right direction.
At some point you will probably end up with different size main jets front to back to make the plugs look right, but you have to get there first.
Ahhh. That doesn’t make sense to me. But if that’s the way you are suppose to do it. Then that is what I’ll do! My theory would be testing wot would be tough since you have to go through the other settings to get there and it would mix.

but I get you want top end to be perfect and then others can follow.

even with the front being lean it doesn’t make sense with all the liquid spitting out that exhaust? Like must be misfiring and pushing the liquid out?
 

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1999 Shadow 750 ACE VT750CD3 Modified
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Look at it this way.
The main jet size effects the needle jet flow as it is screwed into the bottom of the tube where the fuel is sucked up and the the needle jet and jet needle can't really be tuned until you get that nailed down.
 

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Discussion Starter #16
Look at it this way.
The main jet size effects the needle jet flow as it is screwed into the bottom of the tube where the fuel is sucked up and the the needle jet and jet needle can't really be tuned until you get that nailed down.
That makes absolute sense to me now! And I did some reading after reading your post and I’ll be doing the steps that you recommend.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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That front plug looks not too bad, the back one looks either fuel wet or oily which is strange.
What does the other rear plug look like? Is it oil or gas? Does it spark?
 

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Discussion Starter #19
That front plug looks not too bad, the back one looks either fuel wet or oily which is strange.
What does the other rear plug look like? Is it oil or gas? Does it spark?
All four have good spark. At least when I take them out and test them on the block.
289171

it’s a dry soot. The pic above does look wet. But maybe it was a weird angle at which I took the pic.

It rides great. When new plugs are in. But after going for a 10 min ride and gunning it from 1/8 to 1/2 it sputters like a vacuum leak. But have checked with a unlit torch and have found nothing. I could gun it before the 10 mins and no spudder
 

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1999 Shadow 750 ACE VT750CD3 Modified
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I always check for boot leaks with spray carb cleaner, it might be worth a check after it has warmed up for those 10 minutes to eliminate that.
A mechanic I learned a lot of stuff from used to use a acetylene torch.

If that check doesn't show anything unusual I'd up size the pilots to 38's and reduce the main jet on the rear cylinder by one step and see what happens.
You have boot burner or backdraft pipes on that don't you?
 
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