1. Forum
  2. Discussion
  3. Ask a Question!
  4. VT1100C3 misfire and backfire.

Participants

VT1100C3 misfire and backfire.

  • Arthur Blennerhassett

    Help. Please. VT1100C3 216000kms, original unmodified.

    Bought on good Friday. Did 400 of the best kms ever, no faults, very comfortable. 

    Twice, at just over 200kms from full, intermittant backfire. Switch to reserve, keep riding to the next gas station. 

    Only took 12 litres. Then on Sunday, crusing at 100km/h engine cut. Pull to side of road, put on reserve. Starts and limp home. Honda had recoated the tank with the petcock filter still in the tank. 

    Replace petcock, fill tank. Now bike starts but will not rev above 1500 rpm. Suspect fuel starvation. 

    I have replaced the fuel hoses, the fuel pump and the pump relay. Carbs out for clean, but no debris inside.

    Refit carbs, starts well, set balance and mixtures are great at 2.75 turns out. Purrs like a big cat.

    But still won't rev over 1500 rpm, backfire from carbs and exhaust. Can still ride the bike, pulls strong from idle, can do 80 km/h easy, but won't run over 1500 rpm. 

    Has anyone seen this fault before? Thanks for your help.

  • TJ

    @Arthur Blennerhassett Alright brother lets break this down. 

    Heres option 1 which i think is most likely!
    On a VT1100 (CV carbs), above ~1500–2000 RPM:

    • The slides must lift via vacuum
    • If they don’t → engine hits a “rev limiter” feeling wall

    Symptoms match perfectly:

    • Idles fine ✅
    • Won’t rev ❌
    • Backfires ❌ (lean condition)
    • Still “kinda rides” ❌

    Causes:

    • Torn diaphragm
    • Diaphragm not seated correctly during reinstall
    • Vacuum ports blocked
    • Missing/incorrect vacuum line routing

     You said: “carbs cleaned, no debris”

    That doesn’t check diaphragms or slide operation.

    Heres option 2 - Massive vacuum leak

    Less likely but worth checking if you've already done the above! 

    If there’s a big leak:

    • Idle can still be tuned ✔️
    • But transition = ultra lean ❌

    Check:

    • Intake boots (cracks / not seated)
    • Vacuum caps missing
    • Petcock vacuum line (if applicable)

    Option 3 - Fuel flow is still restricted

    Even though you replaced stuff:

    Things to double-check:

    • Tank vent blocked (this is BIG)
    • Inline filters clogged
    • Kinked fuel line
    • Aftermarket petcock flow rate too low

    Quick test:
    Ride it with the gas cap slightly open
    If it suddenly revs → vent is blocked

    Option 4 - Ignition Breaking Down Under Load

    Less likely, but possible:

    • Coils
    • Igniter
    • Plug wires

    But usually:

    • You’d get misfire, not a clean RPM ceiling

    So heres what id do - 

    1. Check CV slides (DO THIS FIRST)

    • Pull airbox
    • Look into carbs
    • Rev bike

    You should see slides lift smoothly
    If they don’t → FOUND IT

    Also:

    • Inspect diaphragms for pinholes/tears
    • Make sure they’re seated perfectly in the groove

    2. Check tank vent

    • Ride with cap cracked open

    3. Spray test for vacuum leaks

    • Brake cleaner around boots while idling
    • RPM change = leak

    4. Verify vacuum line routing

    • Especially if petcock is vacuum-operated

    I hope this helps man! 

    DO FUN SHIT!
    Check the FAQ's here for tons of tuning info and more!! - t.ly/MA6r6

  • Arthur Blennerhassett

    Thank you brother. I had similar thoughts, you made them less chaotic, and put them into a step by step. I will go and do this and get back to you.

    Much appreciated.

  • Arthur Blennerhassett

    Finally got my bike back from the shop. Unfixed.

    The petcock, fuel pump and relay have been replaced.

    Bike still backfires and misfires over 1500rpm. I removed the tank and inlet boot. Both diaphragms move up on acceleration, to full open on full throttle. 

    I have backfire and mostly yellow, some blue flames comming out of the lh carb on acceleration.

    I am going to go buy a plug socket and some fresh plugs. I am expecting black plugs on the rear cyl. Do you have more good advice for me to use in getting this bike running properly? 

    Thank you for all your guidance thus far.

    0 likes
  • Arthur Blennerhassett

    @TJ thank you for your help. 

    I have the answers I was looking for.

    The frount cylinder has low compression. 8 on the guage.

    The rear cylinder is worce. 5.

    Frount plugs are black from overfueling. Black but dry.

    The rear plugs are black and wet from oil.

    The motor is toast.

    The bike is too old to warrant a rebuild. Only a good second hand motor can save it.

    If anyone has a motor or wants a cheap parts bike, let me know.

    Thanks everybody.

  • TJ

    @Arthur Blennerhassett aww man thats a bummer, just an fyi, these engines can be rebuilt pretty darn easily! if youre up to the task. the other option is to get an engin eoff ebay and swap it out with yours. a lot of folks have great luck with that!  

    DO FUN SHIT!
    Check the FAQ's here for tons of tuning info and more!! - t.ly/MA6r6

    0 likes
Please login to reply to this topic!
© 2026, TJ Brutal Customs | Powered by Xenforum