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Symptoms:

The engine speed decreases at a constant throttle position (under no load) - video posted.

Under load, the bike pulls hard at WOT, but does not respond for several seconds when the throttle is chopped off and back on again.

Massive amounts of exhaust popping on deceleration.

The vacuum-operated slides flutter violently at mid-high throttle positions (might be normal?)

When converting BACK to CA-spec stock, same symptoms.

 

Story:

So this is a CA-spec bike (California not Canada).  It ran perfectly OK in its stock form, but I knew it was a little lacking due to the CA-cams having much less lift.  I put in 49-state cams from eBay and it had more power, but got quite a bit hot (50-75% of temp gauge, rather than 25-50% with full CA-spec) and popped on decel.  I checked the valves when doing the cams, synced the carbs with a carbtune manometer setup, and the A/F screws are at ~2.5-out.  The heat and popping indicated a lean-running condition to me, so I pulled the carbs and changed the main jets from 128/125 front/rear to all four 130.  However, at this point I got carried away with converting this bike and removed the PAIR and the EVAP systems.  Before I removed the PAIR system, though, I pinched the lines that ran from #2 and #4 intake runners to the PAIR diaphragms and only noticed a bit more exhaust popping.  Used block-off plates with Hondabond for the PAIR, and capped all EVAP lines and PAIR->Airbox with rubber caps from the auto parts store.  (Four carb vent lines that went to the charcoal canister, one on carb #1 that controlled the EVAP -> vent lines to charcoal, four intake runners (two had PAIR on them), and left the angled port at the back of the carb open to atmosphere instead of connecting to the charcoal canister).  After this, it ran with all the symptoms described. 

 

Efforts:

Took the carbs apart, verified that the float seals are sealing by pressurizing the fuel inlet.  Checked float heights, all 13.7mm.  Checked pilot jets (#40s) and passages with carb cleaner and pressurized air, all clear.  Took out the slides and vacuum diaphragms, all were seated correctly and have no tears or holes - soft rubber.  All slides fully open and close simultaneously when some air pressure is applied to the carb line that runs to the secondary air filter.  Ran various throttle positions while looking down the air inlets (airbox off) and looked like relatively the same fuel flow in each throat.  Removed the air-cutoff valves in the carbs and tested that they can hold vacuum and correctly restrict flow with vacuum applied.  Bypassed the fuel pump and had the same symptoms.  The fuel filter and spark plugs are also new.  Used some silicone vacuum grease on the carb boots: they're clean and still soft rubber.  Sprayed carb cleaner on all ports and joints while the engine idled, no change in engine speed.  I've tried running the bike with several combinations of vacuum lines unplugged and smog equipment reinstalled - even to the point where everything except PAIR was back on the bike, and it still was showing these symptoms.  ... Now that might indicate that removing PAIR was the problem, but I did clamp its vacuum activation lines without any issue with how the bike ran early on. 

 

Ending remarks:

What this feels like is a massive vacuum leak.  I can't figure out where it might be by spraying carb cleaner in all the joints and caps.  On these forums, I've read a lot of "rip that crap off!" in regards to CA emissions components, and that's what I had in mind, but I have to be missing something very important.  I've read through every topic I could find related to the CA smog stuff and PAIR, and I'm currently at a loss for what I missed.  I'm hoping someone with more experience with these bikes (or these forums) can chime in and find something glaringly obvious with what I've written above. 

 

This question always comes up:  WHY DID YOU DO THIS?  I wanted to eliminate the possibility of old vacuum lines causing leak issues, I needed to sync the carbs and these lines were in the way, plus I have a habit of getting rid of things that don't need to be there (i.e. works fine without these things on the Canadian model... but it looks like I could be mistaken...) I'm not looking for more power or significant weight reduction - I know those numbers are negligible in comparison.  Huge thanks to anyone who reads this and more thanks for contributing any ideas as to what might be going on.

 

Symptom video:  Note the throttle position is CONSTANT

https://www.youtube.com/watch?v=V8-wztZl7JA

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  • Member Contributer

Could be worth checking condition of sub-air filter, I once put a “better” (denser) piece of foam in my ‘95 & it took me ages to track down why it was running so weird. Restricted the air flow to the carb diaphragms as it turned out...

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  • Member Contributer

replaced mine as the original went all 'mushy" and sticky maybe worth replacing anyway

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Thanks all - I forgot to mention that I did replace the foam in that filter with some low density stuff, and also tried running without it attached and had the same symptoms. 

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  • Member Contributer

" . . . and left the angled port at the back of the carb open to atmosphere instead of connecting to the charcoal canister). "

 

What happens if you cap off this port? 

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Blocking that port does not allow the engine to rev up at all.  That one is the No. 6 Tube in the attached diagrams.

 

To me, it looks like when the intake runner (No. 10 Tube) is pulling vacuum, that allows free-flow between the carbs and the charcoal canister via this No. 6 Tube (Tees into No. 4), and I think it's just open to atmosphere on 40-state bikes. 

Tube number diagram.png

CA vacuum diagram.png

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check to be sure the evap canister doesn't contain any liquid fuel.  i suggest you take the problem to VFRW also for possible answers.

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Would like to update that I've readjusted the a/f screws with the bike running and it's drastically improved!  I did the ol' turn-while-idling-and-wait-for-response method.  3/4 carbs were fine at the factory setting of 2.5-out, but one of them surged up in rpm at around 3.0-3.5-out.  It's bizarre how sensitive these things are, but at the same time, turning them all to like 4 or 5-out makes no difference to idle (it's very hard to tell when they're actually turning).  As far as I can tell, the rest of the carb system operates correctly.

 

The outcome could have come from two obvious directions... or both.

1. My bike never had all the a/f screws all at 2.5-out - I removed them and cut slots to adjust them, put them to 2.5-out, but didn't take note of what they were initially. 

2. One of the carbs has a vacuum leak that requires a richer a/f mixture to compensate.

 

It's not perfect yet, still feels a bit lean, but it's rideable! 

Thanks everyone for your replies.

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it's risky to have screws out too far as that reduces spring pressure, and screws can vibrate enough to fall out.  you need to find and fix the air leak, not compensate with an adjustment.

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