Rpms stop at 5k when accelerating under load

[D0wn5h1ft]

Those pods look like the cheap ones with the lip that covers the jets on the carb intake bell.

That's why I moved to the velocity stacks to try and isolate that variable. I'm going to go get a set of NGK plugs like I had on my old '78 and hit those with a nice plug chop and see what color they turn out.

To answer the question if I killed it 5k rpms. I did have to pull into a parking lot and I couldn't maintain that range 100% of the time in the city where I live (stop signs, road laws, etc.) but I don't know if it is till a good representation that of that. Also, eventually when the bike built up enough momentum it would pull through that zone and not hit that "wall" anymore because the load wasn't high enough.

To me it still sounds like the mixture is too rich but I don't have a ton of experience with tuning carbs. And what makes less sense is that velocity stacks plus open pipes with stock jetting would be the correct setup.

[Schming]

To me it still sounds like the mixture is too rich but I don't have a ton of experience with tuning carbs. And what makes less sense is that velocity stacks plus open pipes with stock jetting would be the correct setup.

IMHO, you'll get your best results with your carbs set up stock, synched, color-tuned (even if by ear).

Changing the air flow in & out won't compensate for poorly tuned carbs.

[D0wn5h1ft]

I did some searching on the forums while I'm waiting on some jets and plugs to come in and I stumbled across this:

http://www.xs11.com/forum/showthread.php?t=40830

Does that 1980cm400t guy have a point about the carbs running richer due to the points that he outlined? He has a very similar setup to me (not by choice because I tried putting a baffled exhaust on) and it sounds like he had very similar problems.

[motoman]

To answer the question if I killed it 5k rpms. I did have to pull into a parking lot and I couldn't maintain that range 100% of the time in the city where I live (stop signs, road laws, etc.) but I don't know if it is till a good representation that of that. Also, eventually when the bike built up enough momentum it would pull through that zone and not hit that "wall" anymore because the load wasn't high enough.

Still got the same thing goin' on with the Venturer, with intake/exhaust stock and original. Would run above 5K on the 'slab' with gradual load going to the ToyRun today without hitting that 5K 'wall'. Idle up to 5K, smooth as silk with no stumbling or mis-fire. Outside temp. was 20F. Still gonnna have pull the carb bank again and go through them AGAIN as something obviously got overlooked. Enricher has minimal effect on idle at cold start-up, so that's a clue that circuit still has a partial restriction somewhere.

The main circuit is most likely to have a similar restriction that's been missed from the Venturer dielema thread I had started a while back. I'll be posting on that thread in the future when i get it resolved, as the top-end pull has previously over the decades always been exceptionally quick and smooth well above red-line. For now, a hot cup of mojo fits the bill better with this cold weather.

[Mathh]

Don't know if it is of any help to you and I see you already ordered some new ones:
I once had the same problem after fitting four new spark plugs. After weeks of searching i decided to put in the old ones and the problem was gone. Turned out all the new plugs in the box were defective.

[D0wn5h1ft]

To answer the question if I killed it 5k rpms. I did have to pull into a parking lot and I couldn't maintain that range 100% of the time in the city where I live (stop signs, road laws, etc.) but I don't know if it is till a good representation that of that. Also, eventually when the bike built up enough momentum it would pull through that zone and not hit that "wall" anymore because the load wasn't high enough.

Still got the same thing goin' on with the Venturer, with intake/exhaust stock and original. Would run above 5K on the 'slab' with gradual load going to the ToyRun today without hitting that 5K 'wall'. Idle up to 5K, smooth as silk with no stumbling or mis-fire. Outside temp. was 20F. Still gonnna have pull the carb bank again and go through them AGAIN as something obviously got overlooked. Enricher has minimal effect on idle at cold start-up, so that's a clue that circuit still has a partial restriction somewhere.

The main circuit is most likely to have a similar restriction that's been missed from the Venturer dielema thread I had started a while back. I'll be posting on that thread in the future when i get it resolved, as the top-end pull has previously over the decades always been exceptionally quick and smooth well above red-line. For now, a hot cup of mojo fits the bill better with this cold weather.

I have a funny feeling something odd is going on with the fuel metering related to the diaphragm slides. It makes me wonder if we somehow changed the springs in some way when we disassembled the carbs making it so the needles don't properly meter the fuel at the right rpms.

[D0wn5h1ft]

Take a look at this motoman, I'll pm it to you too just in case you don't see it.

Very interesting read, I'd like to see if TopCat would like to weigh in on this one.

http://www.xs11.com/forum/showthread.php?t=20389

[Schming]

I have a funny feeling something odd is going on with the fuel metering related to the diaphragm slides. It makes me wonder if we somehow changed the springs in some way when we disassembled the carbs making it so the needles don't properly meter the fuel at the right rpms.

A vacuum synch will even them out if you did mix the springs up when reinstalling.

[motoman]

Take a look at this motoman, I'll pm it to you too just in case you don't see it.

Very interesting read, I'd like to see if TopCat would like to weigh in on this one.

http://www.xs11.com/forum/showthread.php?t=20389

Hi DOwn5hift,
U sure those plugs didn't get swapped with mine? Was what mine looked like identically after returning from local ToyRun yesterday.
Initially, was a 7mile run on the slab @75mph (20F), then the 20-30mph parade style and same back to mancave through subdivision.
In all seriousness though, even though both our bikes are producing same symptom results, the root of the issues is highly likely to be apples and oranges.

[skids]

A vacuum synch will even them out if you did mix the springs up when reinstalling.

I don't see how the diaphragm springs and higher rpm issues will be resolved with synching the carnies. Maybe I missed something here...

[D0wn5h1ft]

I don't see how the diaphragm springs and higher rpm issues will be resolved with synching the carnies. Maybe I missed something here...

From what I understand sync really only has to do with idle/low rpm performance. When the butterflies are all the way open it's not going to matter hardly at all if they are off by a small amount, especially because mine were bench synced fairly precisely using trbig's technique.

[Rasputin]

From what I understand sync really only has to do with idle/low rpm performance. When the butterflies are all the way open it's not going to matter hardly at all if they are off by a small amount, especially because mine were bench synced fairly precisely using trbig's technique.

In all honesty the synch will do wonders for your bike. If you have not done it you may as well be dipping a pencil in a five gallon pail! Will it affect the diaphragm springs? I do not think so. Will it effect the rest of your problems, well it may help. The one thing that a properly done synch will tell you is if you have problems in other areas. Do a complete synch, then post back. If the guys on this site are as knowledgeable as I think you will find the answer.

[D0wn5h1ft]

Well, I think I found a small vacuum leak between carb bodies #2 and #3. I don't know where it is but I think it is one of the butterfly shaft seals since the boots are in good condition and I have good clamps on the velocity stacks and boots.

I sprayed carb cleaner between the carb bodies and I got a very very slight jump in RPMs (maybe 100-200). It's really inconsistent because it's hard to hit the same spot due to the gas tank covering any good line of sight.

Could a small vacuum leak really be responsible for a high rpm stumble? It seems as though that would be more of something that would affect the idle range more so than with the throttle wide open.

[D0wn5h1ft]

I found this on choke plunger seals:

http://www.xs11.com/forum/showthread.php?t=37346

I'm thinking about ordering some new ones and trying this out. Seems like a very very similar issue. An easy swap while I'm figuring out some time when I can get with Mac for access to his vacuum gauges.

[Schming]

I don't see how the diaphragm springs and higher rpm issues will be resolved with synching the carnies. Maybe I missed something here...

It doesn't matter if the springs got mixed up and didn't get installed in thier original carb bodies on D0wn5h1ft's carbs because the barrels slide from the pressure difference coming through the venturi.

That pressure difference happens when the butterflies are opened thus lifting the barrels.

Unbalanced butterflies cause the cylinders to stumble over one another at any rpm.