Problems with aftermarket carb kit
I've been having intermittent problems with my Superhawk. I get it running well and a few days later or a trip to the track and it starts running poorly again. It's definitely a carb issue.
I bought the bike a few months ago and it had been sitting for a few years. It had aftermarket MIG exhaust, K&N air filter, and Micro Jet kit installed. The jet kit included new needles and mod (3 holes) to the lift holes. After a thorough cleaning and tuning and balancing, it started reliably, ran excellent above 3500rpm, but still sputters a bit below. I replaced the mains with size 48 jets and this made it run better down to about 2500rpm, but still sputters a bit below. Last weekend I went to the track (Summit Point) and it ran great until the late afternoon. Then it started missing and had no power above idle. I would idle fine but cough every time I twisted the throttle. If I slowly apply throttle it would only climb to about 3000rpm before missing. Pulling the choke would kill it instantly, so I'm thinking maybe I sucked something in the intake, but I found no intake clogs or issues. I opened the air box and ran it open but it's still missing. That was my second trip to the track and second time it started running poorly after a few sessions so I'm losing confidence it the SH's reliability. This weekend I decided to go back to a stock carb setup and just tune via shims on the needles. I bought all stock replacement parts on Partzilla last month. I opened the carbs today and found that the stock carb slide springs are TWICE as long as the one currently installed. Can that be right? I double checked the part numbers on Partzilla and the long stock ones match. It's hard to believe the stock springs a so much longer so I'm checking in with the experts here. Any advise? |
1 Attachment(s)
Hers a pic of the stock (long) slide spring and the Micron (short) spring along with the stock part numbers.
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Yes the stock springs are slinky like long compared to aftermarket ones
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Don't lose confidence in reliability due to carb tuning issues. I've owned mine just shy of 10 years and it recently turned 30k (which isn't a high number compared to some guys here) and has been 110% reliable.
So if someone modded the lift holes, you can't really go back to stock, yes? |
Originally Posted by Wolverine
(Post 397740)
So if someone modded the lift holes, you can't really go back to stock, yes?
- I epoxied lift holes on forward carb so now I have only one lift hole. - I epoxied one lift hole on the rear carb so now there are two. - I shimmed the rear needle .020 in. It started right up and after a few minutes warm up, I set the idle and sync'd the carbs. It seems to be running well now. I took a short ride but it's starting to rain so it was very short. Idling in 2nd and 3rd around the neighborhood and it's not coughing - that's good. I took it out on the main road and opened it up a bit - seems good but maybe a bit less power than before. It's hard to say after only a short ride. It's definitely running better and no missing or coughing but I'll take it out again tomorrow before I close the book again. |
Sounds like you're headed in the right direction.
Can't complain though, we really needed this rain. It also knocked the edge off the sweltering heat. |
Just to add a bit more detail on the needle settings...
The carbs have Micron jet kit needles. The profiles look stock but that are adjustable and have 6 grooves. I had not changed the needle settings at all because I figured before the bike sat, it was probably running and I have the receipt from the PO having paid a motorcycle shop to install the kit. Until today both needles were set with the clip on the 3rd grooves and a thin washer beneath each. Today I added another thin washer beneath the needle on the rear carb. I did not change the springs back to stock yet. |
As an update to this thread, I did finally get the SH running perfectly now. I had to remove and clean the carbs again - not sure what was stuck in there, but I suspect a little bit of foam from the EGR tubes. I found bits of that same foam inside the carb slides. I have the K&N air filter and EGR block-offs. Now, I've sealed the block--offs in place to prevent intake leaks.
I also did the COP mod last month. It's a very easy mod and cleans up the wiring nicely. I've been to 4 track days since the repairs and the SH has performed very well. I'm still struggling with a slightly slipping clutch. I'm certain it just needs to be bled more, but it's a total PITA. Now I'm looking to get a bit more power or lose some weight or both. I'm looking at doing a 520 conversion next and adding a couple of teeth to the rear sprocket. The stock gearing is just so tall. |
Try timing advance, either 2 or 3 degrees. Sync your carbs a couple times a year too.
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Originally Posted by Braymond
(Post 398714)
I'm still struggling with a slightly slipping clutch.
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