Weird issue

[Mekanix]

Having issues with the gsx.

Runs great after 5k or after the raves open.

Bellow that its very rough and misses allot. Like there is a wall just before 5k.

This is new and I'm not sure what to do or what else to try.

Tried:
Setting pop off again to 38
Cleaned carbs
Pressure checked fuel lines, selector, water separator from the baffle to the carb.
Return line is clear
Changed coil because it was easy and felt like a possible electrical miss.
Set raves for 4500 open (flush with caps)
Every possible low speed screw setting (doesnt fix anything just causes other problems so set to 1 turn out)
Synched the two carbs with the idle all the way closed.

Thinking maybe water regulator? Not sure what one of those failing feels like.
Maybe pickup coil
Maybe cdi dying
Maybe regulator
Feels electrical or maybe a an air leak or really bad carburation

I don't know where to look.

 

[Strizzo]

Hard starting too? Had similar issues when my needle levers were set wrong and the diaphragm was holding them open and the o rings on the seats were leaking AND the restrictor wasn't in the . It would idle and run kinda ok once started but was really rich and would flood immediately if I shut it off.

 

[Coastiejoe]

The issue you are having is not the normal result of a regulator, however, they cause very weird things when they fail. Simply unplug it, if the problem goes away, replace it. This is a nice simple and free test. So wroth giving it a try.

 

[Mekanix]

Hard starting too? Had similar issues when my needle levers were set wrong and the diaphragm was holding them open and the o rings on the seats were leaking AND the restrictor wasn't in the . It would idle and run kinda ok once started but was really rich and would flood immediately if I shut it off.

Tried pop off test once the carbs were assembled and they held pressure.
Doesn't have hard starting issue but that could be because I was testing other things at the time. It was always an instant fire up even after running it at 5k for a minute and doing plug chop.

I actually tried setting the pop off to 43 and that caused some really weird stuff. I could jump out of the hole with no trouble at all. Plugs were nice and tan. But run wot for more than a second and it would bog out as if it ran out of fuel. After that I wait a second and I could do that again.
That's when I set the pop off back to 38, now it will run wot as long as I hold it but tops out at 6850 after holding it 4 seconds.

Seems like between 1/4-1/3 throttle that it happens.

I'm also running the rotary valve advanced because it was impossible to set properly. Its at 142 right now. Thing is that right after the rebuild everything seemed ok at 3500 and up so I think the rotary valve timing might not be a problem since it ran good at that setting and then this issue started.

 

[Mekanix]

The issue you are having is not the normal result of a regulator, however, they cause very weird things when they fail. Simply unplug it, if the problem goes away, replace it. This is a nice simple and free test. So wroth giving it a try.

Yeah I would have expected a limiting factor but then again my battery is very good and might be taking up the AC ripples.

I can pretty much hit the gas and go, as long as its reving fast through the bad spot and get's above 5k Its great and responsive but if I go up slowly or come down below rave opening it gets rough and misses allot.

First on my to do list next time out is the voltage regulator and maybe mpem and then....

I'll try and take a video to dissect for next time.



It's always had a rough low end. But it was just bad before 2800, from 3000 on it was always smooth running with only a few misses that I knew were normal.

 

[suke]

I have a similar problem. I adjusted my raves in by 1 turn from flush and it pushed the bog into the lower rpm range. Good luck finding it! My plugs look good and if I try and give it more gas via primer it about dies so it's not lean. So I'm just going to ride and enjoy.

 

[Sportster-2001-951C-Stock]

Tried pop off test once the carbs were assembled and they held pressure.
Doesn't have hard starting issue but that could be because I was testing other things at the time. It was always an instant fire up even after running it at 5k for a minute and doing plug chop.

I actually tried setting the pop off to 43 and that caused some really weird stuff. I could jump out of the hole with no trouble at all. Plugs were nice and tan. But run wot for more than a second and it would bog out as if it ran out of fuel. After that I wait a second and I could do that again.
That's when I set the pop off back to 38, now it will run wot as long as I hold it but tops out at 6850 after holding it 4 seconds.

Seems like between 1/4-1/3 throttle that it happens.

I'm also running the rotary valve advanced because it was impossible to set properly. Its at 142 right now. Thing is that right after the rebuild everything seemed ok at 3500 and up so I think the rotary valve timing might not be a problem since it ran good at that setting and then this issue started.

I view pop as a low speed adjustment despite it can affect high speed as well. To avoid interfering with high speed performance I set pop-off by simply changing the spring as opposed to manipulating the arm. In most every case I can recall, this produces a reasonable enough result for my satisfaction. If the arm is bent too far down (to try increasing pop) there may not be enough arm travel remaining to lift the metering needle fully off the seat. I've seen hard cold and even warm starts caused by a bent arm, the metering arm cannot move far enough to lift the needle off the seat under lower vacuum conditions. So if this is occurring, it makes me think the arm geometry is wrong in a big way.

Okay but what is the pop pressure you're shooting for and what are the spring rate and orifice sizes you're using? If the metering arm geometry is incorrect, it can have an impact on high speed operation, which it shouldn't have.

Here's the chart I use to spec my pop pressure, based on the original factory specified components:

 

[Mekanix]

1.5 and 80 gram. Funny thing is that with that combo I get a pop off of 23 and I have to bend the lever a bit to get it up but its quite bent by the time it gets to 38 so I scraped that route.

The best thing I could do was stretch some old 80 springs on the ends to get up to 38 because I tried to keep the arm flat and stock. That seemed to work and its always worked that way so I'm leaning away from pop off as the culprit for the moment.

Also the needle and seat are not leaking. It holds quite well.

I tried a combination of every spare part I have but the results were always less than the chart says it should be.

 

[Sportster-2001-951C-Stock]

Then say for instance you wanted to experiment with a higher pop than 38psi, say maybe 43 psi? The correct way to increase the pop would be to remove the black 80gr spring and replace it with a 95gr spring.

 

[Sportster-2001-951C-Stock]

1.5 and 80 gram. Funny thing is that with that combo I get a pop off of 23 and I have to bend the lever a bit to get it up but its quite bent by the time it gets to 38 so I scraped that route.

The best thing I could do was stretch some old 80 springs on the ends to get up to 38 because I tried to keep the arm flat and stock. That seemed to work and its always worked that way so I'm leaning away from pop off as the culprit for the moment.

Also the needle and seat are not leaking. It holds quite well.

I tried a combination of every spare part I have but the results were always less than the chart says it should be.

I'd say if you have an undamaged 80gr spring with a properly shaped metering arm, and pop measures 23psi then the seat orifice must be 2.0

In this case you could install a smaller seat to reach 38 psi, as opposed to bending the metering arm to such a position it may not work well.

Some guys go through the trouble of bending the flat part of the arm even, to make it so it's perfectly parallel to the diaphragm, then they polish the surfaces where the diaphragm button and top of metering needle contact the arm. Besides replacing the metering needle daily and polishing the brass seat, that's about the limit of how anal it can get, LOL.

 

[Mekanix]

Then say for instance you wanted to experiment with a higher pop than 38psi, say maybe 43 psi? The correct way to increase the pop would be to remove the black 80gr spring and replace it with a 95gr spring.

Tried 43 with the arm bent and I think that caused a problem with not allowing enough flow. That lead to the chamber emptying under full throttle and not filling fast enough.


Just a hypothetical thought....

When I'm testing for pop off on the mag side I'm using the fuel inlet. The fuel pump diaphram is going to be subjected to 30-45 psi during that test and could stretch maybe ?

Could that have stretched the diaphram enough and maybe the fuel pump is pushing more or less fuel?
As in, Could I have done damage this way?

 

[Mekanix]

I'd say if you have an undamaged 80gr spring with a properly shaped metering arm, and pop measures 23psi then the seat orifice must be 2.0

In this case you could install a smaller seat to reach 38 psi, as opposed to bending the metering arm to such a position it may not work well.

Some guys go through the trouble of bending the flat part of the arm even, to make it so it's perfectly parallel to the diaphragm, then they polish the surfaces where the diaphragm button and top of metering needle contact the arm. Besides replacing the metering needle daily and polishing the brass seat, that's about the limit of how anal it can get, LOL.

lol

Nope its a new 1.5mm seat. I have 4 of them and two 2.0's to play with. If I put a 2.0 in there it drops to 15 psi. Thats with the 80 g springs and flat new arm.

I'm starting to think maybe the carb body's are modified or just worn.


Thinking of shimming the springs up to compensate and see if that brings things inline with the chart. I could see having to make up for 2-3 psi by bending the arm but so far its looking like the problem is somewhere else.

 

[Sportster-2001-951C-Stock]

So if you're trying to keep the 1.5 seat and want 38 pop the black spring should do that for you. If it didn't I'd suspect the arm is mishapen first, or something's wrong with the spring.

I think you should be able to get the arm bent back to where it should be, just make sure it's not too tight on the swivel shaft it might bind, then get a few new springs and you should be able to get within a few psi of Mikuni's chart. Mikuni didn't dream up this chart I don't think, I think it's within a few psi of reality.

When you see a pop spec for a 787 that's 32-21, it's pure BS, the reason is Mikuni's chart doesn't give a range nearly that wide, it's more precise than that, within a few psi of Mikuni's numbers.

So I don't have any explanation for why you're measuring 21psi with an 80gr spring except maybe something's bent out of shape.

There are other ways of reducing or adding fuel besides pop (real purpose of the metering arm/needle/etc really is to stop fuel from pouring down your intake), like by adjusting the pilot jet orifice for instance, for off idle mixture. The idle mix screw should have most affect at idle speed, that's what I use that screw for, smoothest idle but a little on the fat side of smooth as opposed to the lean side of smooth.

 

[Sportster-2001-951C-Stock]

lol

Nope its a new 1.5mm seat. I have 4 of them and two 2.0's to play with. If I put a 2.0 in there it drops to 15 psi. Thats with the 80 g springs and flat new arm.

I'm starting to think maybe the carb body's are modified or just worn.


Thinking of shimming the springs up to compensate and see if that brings things inline with the chart. I could see having to make up for 2-3 psi by bending the arm but so far its looking like the problem is somewhere else.

Well, mikuni doesn't specify using a shim in the chart but all's fair in love and war I guess. I mean heck, if you can tweek it so it runs correctly then no big deal how you got there.

Those are SBN's right? That chart is for the SBN line.

 

[Sportster-2001-951C-Stock]

Tried 43 with the arm bent and I think that caused a problem with not allowing enough flow. That lead to the chamber emptying under full throttle and not filling fast enough.

This is exactly what I would anticipate if the arm was bent too far so needle travel is limited.


Just a hypothetical thought....

When I'm testing for pop off on the mag side I'm using the fuel inlet. The fuel pump diaphram is going to be subjected to 30-45 psi during that test and could stretch maybe ?

Could that have stretched the diaphram enough and maybe the fuel pump is pushing more or less fuel?

Yea, I don't know if this might stretch the diaphragm but mylar is tough stuff (thickness counts, of course) but even if the diaphragm is stretched that shouldn't limit it's back and forth motion I don't think.
As in, Could I have done damage this way?

I doubt it caused any damage (my opinion).

 

[Mekanix]

Well, mikuni doesn't specify using a shim in the chart but all's fair in love and war I guess. I mean heck, if you can tweek it so it runs correctly then no big deal how you got there.

Those are SBN's right? That chart is for the SBN line.

Yeah stock sbn's by the look of them and all genuine parts.

I tried all the arm's I have in both carbs and all give a lower pop off than spec. Stretching the springs does help and bending the arm too much does work to but its not right either way. I think a shim would help bring the baseline to a normal.

Before all this started though I had a set of stretched 80 g springs that poped at 38 psi right on and the midrange around 3000-4500 was nice and smooth.

But I'd started to notice there was this point just before rave opening where the rpm's would flutter slightly before the raves just opened. To fix that I just lowered the rpm for rave opening and that problem went away.
Now though Its gotten worse. Almost like something has been failing slowly and now is terrible.

 

[Mekanix]

Yea, I don't know if this might stretch the diaphragm but mylar is tough stuff (thickness counts, of course) but even if the diaphragm is stretched that shouldn't limit it's back and forth motion I don't think. I doubt it caused any damage (my opinion).

How do you check pop off on the mag carb with the fuel pump attached ? Guessing the same as I did?

Also the pump does hold pressure to 5 psi pretty much as long as I leave for.

 

[Sportster-2001-951C-Stock]

Yeah stock sbn's by the look of them and all genuine parts.

I tried all the arm's I have in both carbs and all give a lower pop off than spec. Stretching the springs does help and bending the arm too much does work to but its not right either way. I think a shim would help bring the baseline to a normal.

Before all this started though I had a set of stretched 80 g springs that poped at 38 psi right on and the midrange around 3000-4500 was nice and smooth.

But I'd started to notice there was this point just before rave opening where the rpm's would flutter slightly before the raves just opened. To fix that I just lowered the rpm for rave opening and that problem went away.
Now though Its gotten worse. Almost like something has been failing slowly and now is terrible.

There were SBN carbs that used shims, but I think those were odd-ball setups using the 115gr spring or something. I see nothing wrong with using a shim if that's what it takes, better than modifying the spring (not a huge sin but not better than shim IMO) or bending the arm so WOT venturi no longer fuels properly.

Kinda though maybe you could lean it enough with a tighter pop, might take a smaller jet instead.

 

[Sportster-2001-951C-Stock]

How do you check pop off on the mag carb with the fuel pump attached ? Guessing the same as I did?

Also the pump does hold pressure to 5 psi pretty much as long as I leave for.

Yep, that's the same way I check pop, right through the fuel pump. I think that's the same procedure Mikuni specs.

I guess you mean the diaphragm hols pressure. That's all it needs to do, besides move back and forth with the crankcase pulses. I don't think it's pumping too much fuel, never heard of that before.

Order some smaller jets if you think mid range is too fat, that's what I'd do.

 

[Sportster-2001-951C-Stock]

Ha, talk about trying to make changes in the right place... I advanced a cam 3* yesterday that was at gear zero b/c idled rough and vacuum was low. The result was a much better idle and didn't notice any power loss.

 

[Mekanix]

Yeah I hear ya. Just wish this one would have something I could change that would improve the problem rather than cause something else


I think I have 70's in there right now.
Going to try 65's to see what happens when I get the chance


So far I'm going to try unplugging the Regulator seeing what that does but first I'll check the voltage for any AC.

Then maybe disassemble the water regulator because I found some water dripping out of there and some under the cap.



What would happen if the water regulator was always pushing out too much water or what would happen if it was clogged and not putting out any water?

 

[Sportster-2001-951C-Stock]

If there wasn't enough water I think your hole shot would stink and might burn through exhaust hose that connects to the waterbox from the cone pipe. If too much water would probably limit WOT. Not sure if it would make it run too rich, never heard that complaint before, usually lean hesitation is the issue with our carb motors as small passages tend to clog with trash and gum, white death corrosion and such.

 

[Sportster-2001-951C-Stock]

Come to think of it, there was a 2-stroke XPS at the island where we hang out last Saturday and it was a little rich off idle, could hear it 4-stroking.

 

[Mekanix]

That's what this feels like. Rich on low end but it was manageable since it Used to smooth out after 3k and that's the lowest RPM I would use while cruising anyways and now its only good after raves open.

 

[Sportster-2001-951C-Stock]

Yeah, that guy's ski was rich down low too but not real bad, maybe a little more than my boat. Pretty sure it was a 787 but can't say for sure absolutely b/c I didn't look inside or get that close. I'd say he coulda used a jet one size smaller and maybe not had a hesitation issue.

I think it's worth trying, what's to lose?