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Discussion Starter · #1 ·
I don't make a habit out of this, but the other day I was taking a left turn and tried to give it a lot of throttle while below 2k. It felt completely gutless. But then like someone flipped a switch, the power came back. Closest thing I can relate to is when I've run out of gas at cruising speed, flipped over to reserve, and the fuel started flowing again. It's that abrupt of a change in power. It's not even a random misfire. It's like all power is gone.

I had this happen a couple of weeks ago when I was testing a WOT pull in 3rd gear. I wanted to pull from 2k to redline. When I grabbed the throttle, there was nothing there. I grabbed a 2nd time and nothing. I eased it above 2k and grabbed again and it took off like I would have expected. It's not the feeling of coming into the power band. It either has power or it doesn't. I don't know if the carb slides are sticking or something? I've only had it happen with a quick snap of the throttle at lower RPMs. I haven't had any other issues when I'm riding.

The engine is warmed up and off choke. It runs fine with light to medium throttle at that RPM, and it's not even every time at heavy throttle. Specifically <2k and a quick heavy throttle causes it.

(Side note: I typically limit my throttle until at least 2.5k if not 3k, as I don't want to lug the engine).
 

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First paragraph sounded like a clogged pilot, but then it's not consistent.

Still seems like a fuel issue, maybe erratic slides. Pulling the choke might prove it's a fuel issue, if you can catch it consistently bogging.

Earshave or not?

Is this also happening with the stock timing? Or only with the custom profile?
 

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Discussion Starter · #3 ·
No earshave. It happens regardless of timing setting.

I do have the two carb vacuum ports linked with 7/64" hose, but the vacuum ports are behind the throttle and SHOULDN'T affect the slide operation.
The vacuum that the slides operate on comes from between the slide and the throttle plate.
However, it's possible there's a strange resonance between the two carbs, causing erratic slide behavior.
I could disconnect the link to see if that resolves it. I have to finish out my current tank of gas first to compare MPGs, before I can change things.
 

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Discussion Starter · #4 ·
I went for a ride today, and I had no issues. I'm wondering if it was a fluke? Or debris in one or both jets? IDK.
I guess I'll just hope all's good for now!

Thanks!
 

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Discussion Starter · #5 ·
It happened again yesterday. I tried to recreate it while riding Thursday-Saturday with no luck. But Sunday, I rode to a restaurant, parked for about 1hr, and then went home. Engine temp was just above the lowest line on the gauge. As I was pulling out of the parking spot, I had no power, then it all came back. Prior to this, it was idling just fine. It revved up to ~1500 to ~2000 or so (I wasn't watching the tach) as I let out the clutch, but didn't accelerate for a moment. The rest of the ride was uneventful. It was just that one time pulling away from a stop that anything was off.

I was on my modified timing at the time, so I can't rule that out as a problem. Especially since I have it set up to pull back the timing a lot at closed throttle. If the sensor thought the throttle was closed, it would reduce power.

My gut feeling is a slide is catching, but I don't have anything beyond a feeling to support that.

The most frustrating problems are the random ones that can't be recreated!
 

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Would be sort of rare for both slides to stick at the same time, but not impossible.

Random speck of dirt in a pilot jet? Was it still running on one cylinder or just totally died for a moment?
 

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Discussion Starter · #7 ·
Would be sort of rare for both slides to stick at the same time, but not impossible.

Random speck of dirt in a pilot jet? Was it still running on one cylinder or just totally died for a moment?
It didn't lose RPM, it just wouldn't gain RPM. So it was probably running on one cylinder at that moment.

I haven't looked in the tank to check for rust/dirt. There's no exterior signs of rust on the tank, and it was well cared for by the previous owner. I also haven't been in the carbs since I bought it last year. Haven't needed to yet. I'm sure I'd need to replace seals if I opened them up.
 

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Discussion Starter · #8 ·
Update: Today it died on me while pulling out into traffic! Fortunately it started right back up before I became roadkill.

I found a way to reliably recreate the issue. A quick twist of the throttle in 4th or 5th gear at 1500 RPM will cause it! This is not something I normally do, but it mirrors the brief conditions during a moderate standing start.

I richened the idle screws 1/2 turn and the lean condition goes away....but so do my decel pops. I'm going to try 1/4 turn richer.

I increased the gap in my rear cylinder spark plugs to 1.15mm (0.045"), and that also helped. During the 1500 RPM acceleration, only the rear cylinder fired. (Wider gaps can burn leaner mixtures). It's a band-aid, but it did help me to diagnose the issue.

It was only 46 degrees when I was last riding, so the issue might go away with increased air temps as well.
 

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I’m no expert but I’m still leaning towards fuel. And I only say this because my bike acts differently depending on temp(air temp not bike) I still haven’t installed the guage I bought from you because I didn’t like the paint I chose.

Point being is on hotter days my idle doesn’t like to come back down as quick.
 

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Next time it happens and your not in traffic, shut the petcock off and see if that wakes it up, you should have a 15 seconds or so of gas.. If it does wake up then your floats sticking. Also try backflushing through the float bowls.
 

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Discussion Starter · #12 ·
I have suspected petcock issues already, so I might rebuild it just to rule that out.
 
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