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Hello, I have an f4 I have been working on for the past year, I just finished rebuilding the motor and working out all the kinks for the turbo I have put on it. The problem I'm having is, when it warms up, it will stall and if I try to start it, it will backfire. It starts and runs just fine when cold. I'm just trying to work out if I'm running to rich, to lean or if the carbs are gummed up (they sat with fuel in them for about 4 months while I was rebuilding the motor). It runs fine at any rpm above 2.5-3k at all temps. any ideas as to what's up?
Way, way better than useless spray carb-cleaners without any chlorinated compounds any more.
Red Line SI-1
Techron Concentrate Plus
3M Max Strength Fuel System Cleaner #08814
Royal Purple Max Atomizer 18000
Gumout All-in-One (may be off list soon due to reducing amounts of PEA)
Completely disassemble emulsion-tube and pilot jet. Poke out all lateral bleed holes with soft copper wire. Dried petrol turns to plastic and cannot be dissolved again. Must be mechanically scrubbed away. Also poke out all bleed-holes in carb-venturi towards float-bowl. Especially the mixture-screw hole.
Bike ran perfectly fine when leaving showroom floor. It will again when carbs are restored to factory-fresh clean with all factory settings.
That's a lot of work and requires lots of experience and equipment. I just send my carbs to this outfit for refurb every winter when I'm overhauling my race bike. Since I run in stock class, restoring carbs to factory-fresh condition is one of "mods" that make HUGE difference compared to others running with clogged carbs causing stumbling and revving laziness.
https://customcarbservices.com
Expert work, reasonable costs and fast turnaround! Bike will run like brand-new off showroom floor!!!
Thank you for replying, was afraid I needed to clean them. It's just very hard to take it apart with how the intake is setup. I'll probably get it cleaned today. I'm currently running about 5 psi of boost but was originally running 10 psi. And as requested, here are some photos.
Think I found the primary cause. In the picture below you can see all around the intake is wet, it's fuel. I think the needles aren't sealing and it's forcing extra fuel into the bike and around the carbs. I'm rebuilding them in a little while so I'll make sure to take pictures of the condition of the carbs.
Needles don't seal. It's gap between needles and main-jet that feeds fuel into carb-venturi and into engine.
That liquid petrol is on outside of carbs! None of that spill will ever get into engine, so it won't affect fueling in any way.
Leak in fuel-rail perhaps? Did you replace fuel-rail O-rings?
Could also be float-bowl seals.
Good job on turbo build! Really good positioning of turbo high so oil-drain can get back into oil-pan without any issues.
Thanks for the reply, I meant the float needles not the jet needle, my bad lol. And actually I was right, one of them was bad. Here's a good one next to the bad one.
The insides of the carbs are way better than I expected, and the jets are perfectly clear, I did clean them anyway Incase your wondering. what's weird is that I put that bad float needle back in and it working just fine. maybe the seats had some varnish on them that came off while disassembling everything. Or one of the bowl seals was bad and that's what was leaking fuel everywhere. Guess I'll find out when everything is back together. And I plan on syncing the carbs as soon as there on.
Well... I have a problem, the bike will not idle. And by that I mean it revs to 6-7 immediately after starting. The throttle looks like it's not closing fully. I'm wondering which way you turn the sync screws to fix this issue.
Backfire while attempting to start.
