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Fuel screw & jetting

Old 06-06-2018, 08:27 PM
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Fuel screw & jetting

Ok I am starting a new thread. I just cleaned my carbs, fixed the chokes and added Jack Flash thumb screws.

I have the front at 2.75 turns out and the rear at 2.5. I am getting crazy popping on decal, even more than at stock setting (which I don't know what that was)

I am also getting major carb farts now on the front cylinder.

As mentioned in my other thread my buddy thinks that the carb farts are from ever so slightly bent valves. I am not sure since its a very intermittent problem.

What setting for fuel screws is working for guys with good running bikes? I have 2 bros carbon slip ons.

Also what jetting or even point me to a jetting thread I can read.
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Old 06-07-2018, 06:14 AM
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Bent valves....don't think so. Though someone really should write up a jetting thread =)
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Old 06-07-2018, 07:15 AM
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Yeah that was a diagnosis with him in Maine and me in NY. I am not thinking bent valves anymore. Still chasing the issue but its for sure carb fart back thru the front carb. Attempting to richen front cylinder. Also gonna put a longer trumpet on front.

I am looking at this old thread but I have aftermarket needles.
https://www.superhawkforum.com/forum...-set-up-24769/
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Old 06-07-2018, 04:59 PM
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Originally Posted by smokinjoe73 View Post
Ok I am starting a new thread. I just cleaned my carbs, fixed the chokes and added Jack Flash thumb screws.

I have the front at 2.75 turns out and the rear at 2.5. I am getting crazy popping on decal, even more than at stock setting (which I don't know what that was)

I am also getting major carb farts now on the front cylinder.

As mentioned in my other thread my buddy thinks that the carb farts are from ever so slightly bent valves. I am not sure since its a very intermittent problem.

What setting for fuel screws is working for guys with good running bikes? I have 2 bros carbon slip ons.

Also what jetting or even point me to a jetting thread I can read.
Joe, hop on FB and message Bobby Kuhl. I noticed him sharing his carb set-up a little while back. The general consensus there was that the one on here was rich for most everyone.
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Old 06-08-2018, 06:20 AM
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A question concerning decel/closed throttle exhaust popping (afterfire?). I was under the ASSumption that an open exhaust system is going allow popping with no other changes to the tuning of the carbs. That is, take of stock cans and replace with straight through, unbaffeled cans. Also a richer tuning will exacerbate this condition.
I'm, as usual, confused.
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Old 06-08-2018, 10:29 PM
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I am more trying to eliminate the carb farts than the popping, although the popping is obtrusive now. I am sure the richer fuel screw setting is affecting the popping.
May try to bump each carb a half step richer.
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Old 06-17-2018, 02:05 PM
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have you set the TPs yet on the carbs?
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Old 06-18-2018, 05:21 AM
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Hehe, no that is on the list. Had a week in Laconia bike week away from the vtr. Life gets in the way.
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Old 06-18-2018, 07:40 AM
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My Hawk never did pop like crazy before the pair delete. Once I let the choke out a tad and it did it like nuts, I wondered what the heII was going on before realizing why.
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Old 06-18-2018, 11:17 AM
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Wolverine missing what youre saying. Its the pair delete? Its the choke?
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Old 06-18-2018, 12:42 PM
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Yes, the choke was left out just a touch unintentionally. It popped like crazy when I closed the throttle, at any engine speed.
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Old 06-18-2018, 01:12 PM
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Ah ok. So you think richness causes the popping to some degree? I am about to go richer both cylinders to alleviate popping. I had less with the choke on so I think Im too lean.
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Old 06-19-2018, 04:43 AM
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Joe,

From my experience the best thing to do when your bike feels and sounds "Off" is to sync the carbs.

If it's still off do an idle drop and then check the TPS. The mixtures will be roughly right and if necessary you can tweak your Jack mixture screws on the run until the bike feels right.

I have my bike set up rich( A mixture of different brand parts . I wrote the settings down somewhere ) as most of my riding is in open country, however , as we all know on here the vagaries of carburettors can at times cause problems.

I for for one would like to know what settings you arrive at with your carbs to get your bike running perfect in relation to the conditions that you use it under.
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Old 06-19-2018, 06:06 AM
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So yeah was trying to avoid the sync and tps but those are now 1st on the list.

Can someone link me to the Jack fuel screw adjusting procedure as its running?
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Old 06-22-2018, 11:14 AM
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Maybe I missed it but can you give the complete setup including air filter, air box mod, jet size, I just went through this with my new motor setup. To get my bike to run right " new motor " had to go with stock air filter and for now took off the Dr Honda velocity stacks and back to the plastic. but after 500 miles or so will start to revisit the intake side of things before the dyno to see what I have gained by all this.

So my long winded rant is we need your baseline of the bike.

Syncing the carbs and tps setting is the first place to start. Have to having it run the best at whatever setup to know which way to go save you a lot of time.
Always go back to a basic baseline and move forward and analyze the outcome of the change you made.
I am sure there are setups to get you close you where you want to be.

But none of this is new to you "have gotten lots of useful and very knowledgeable info from you in the past"

Last edited by Stumpy; 06-22-2018 at 11:24 AM.
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Old 06-22-2018, 07:51 PM
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So yeah update.
Did the 2 obvious jobs and got HUGE results.
Did carb sync and TPS.
Synce didn't seem way off but got it pretty spot on with my yard stick & clear plastic tube with valves sync tool.
TPS was almost at 800 so got it to 500.
Turned the front fuel screw back in 1/4 turn which puts it at I think 2.5 or 2.75 out.
Last thing I did was put a 2nd long trumpet on the front cylinder. I believe this worked a lot to stop the carb farts but either way I went from way too many farts to almost none.
BIKE IS TRANSFORMED.
Improvements include quick and easier starts, steadier idle, WAY more low end grunt to the point that I accidentally had the front wheel off the ground a lot on the test ride(!)
So I didn't dig into the needles this time but did clean all the jets at the start of this debacle.
I am pretty sure I have a 45 main.
Also at the start I replaced the choke fittings with the jack flash units.
I am very happy to get my bike rideable again. I am wondering about the bent valve possibility my buddy believes so next will do a leakdown test.
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Old 06-22-2018, 09:13 PM
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Popping and back-firing on decel is also caused by an exhaust leak at the head...
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Old 06-23-2018, 05:55 AM
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At the headpipe gasket?
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Old 06-23-2018, 06:49 AM
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Originally Posted by smokinjoe73 View Post
At the headpipe gasket?
Si, Senoir!

Copper tube crush gaskets required, or flip them around with some Hi-Temp Red Copper filled RTV silicone...
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Old 06-23-2018, 08:20 AM
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Aye caramba no es Bueno!
Ok yeah I have some of the copper gaskets around. May be an issue. Gracias el guapo.
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Old 09-22-2018, 08:48 PM
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Just adding the final word on my summer carb tuning/ fuel screws/ TPS/ carb sync.

My bike was carb farting on the front terribly, popping on decal to wake the the whole city and stalling intermittently.

I adjusted the fuel screws out another turn and now all the bad symptoms are gone. Idles fine, not popping and zero carb farts. Hope this helps someone.
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Old 09-30-2018, 04:13 AM
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I just re read this thread and as a veteran of 19 carb pulls I can relate to your experience Joe.

The sad thing is that I did it about 5 years ago and can't remember the settings I arrived at but she goes well under the conditions I ride .

I'm sure that there are no two VTRs on here that are exactly the same, something about the VTR that is different from other bikes is that it adapts well to mods and no matter how small the mod is you can get a measurable change in the bike.

If my bike feels off then I always go the sync in the first instance , and if that doesn't work move onto an idle drop and lastly check the TPS.
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