lean going downhill ...

[maro]

So yesterday was my first longish trip since I got my jetting fairly dialed in. I've been running in all the gears/circuits in all the RPMs just fine..in fact I was going to go up on the pilot as I feel it is a bit too lean...as tend to stay in the low RPM's conservatively.

Yesterday on the turnbike I was running about 80 -85 MPH at around 5200 RPMS for a while and I began to notice the bike jerking from time to tomeas though it was lean. Only really at between 5000 - 5400rpms. I really noticed it going downhills when I would let off the throttle a tad and remain at the same speed.

I'm at 3.5 notches from the bottom on my needle. When I was at 3 notches I was feeling like it was too rich. What should I do here?

 

[tkent02]

I really noticed it going downhills when I would let off the throttle a tad and remain at the same speed.

With the throttles nearly closed you are probably on the pilot circuit at that point, not really the needles. How did you set the mixture screws?
They are perhaps too lean?

 

[maro]

With the throttles nearly closed you are probably on the pilot circuit at that point, not really the needles. How did you set the mixture screws?
They are perhaps too lean?

probably should have thought of that. I guess my confusion was why it was happening only in 5th at that RPM range. I know thats right where the needle is being introduced to the pilot. But I guess being too lean on the pilot makes sense. I have 45's in there now and I am almost 3 3/4 turns out. I have been procrastinating putting in 47.5's Guess it's time.

 

[81gs1100]

it was happening only in 5th at that RPM range. I know thats right where the needle is being introduced to the pilot.

Your carb circuits have nothing to do with an RPM range. They are all throttle position.

If you would like to narrow down a circuit here is a tip..

At closed throttle make a little mark on your grip and put a piece of tape on the bar directly across from it, then goto wide open throttle and put another mark on the grip. Then make a mark between those two marks, and then 2 more marks between each of those. So you have marks at
0 - 1/4 - 1/2 - 3/4 - and WOT.

Now take another ride and pay attention at what throttle position you are having issues.

As far as the leaness when going down hill, I don't know your carbs very well but if they have a fuel shut off circuit I would clean it up and make sure it is clean. The fact that your lean is because you are closing your throttle plate and its affecting the flow of fuel. If you were costing down a hill and shut your throttle completely it would run super lean. (2-stroke nightmare). Some carbs have a fuel shut off circuit that is like a larger pilot that when you close the throttle it can still pull the needed fuel into the engine.

A bigger pilot might solve your problem in that area but may have adverse effects on drivability in other areas.

Is this a common route for you? Or a once and a while trip?

 

[maro]

Thanks for the response. I am familiar with plug/throttle chops. Kinda lost sight / forgot about how it's really all about throttle position. When I was testing the jetting I was just pulling hard through the gear WOT to find my correct main and needle.

I worked from Main setting, to Needle setting to Pilot. Like I mentioned, I've been fairly certain I am lean on the pilot. and cruising in 5th gear at 83MPH at approx 5000RPM I am NOT wot.

The rarely take the highway, however I need to get this sorted as I plan taking some long journeys soon that will require boring slab time.

Your carb circuits have nothing to do with an RPM range. They are all throttle position.

If you would like to narrow down a circuit here is a tip..

At closed throttle make a little mark on your grip and put a piece of tape on the bar directly across from it, then goto wide open throttle and put another mark on the grip. Then make a mark between those two marks, and then 2 more marks between each of those. So you have marks at
0 - 1/4 - 1/2 - 3/4 - and WOT.

Now take another ride and pay attention at what throttle position you are having issues.

As far as the leaness when going down hill, I don't know your carbs very well but if they have a fuel shut off circuit I would clean it up and make sure it is clean. The fact that your lean is because you are closing your throttle plate and its affecting the flow of fuel. If you were costing down a hill and shut your throttle completely it would run super lean. (2-stroke nightmare). Some carbs have a fuel shut off circuit that is like a larger pilot that when you close the throttle it can still pull the needed fuel into the engine.

A bigger pilot might solve your problem in that area but may have adverse effects on drivability in other areas.

Is this a common route for you? Or a once and a while trip?

 

[81gs1100]

Thanks for the response. I am familiar with plug/throttle chops. Kinda lost sight / forgot about how it's really all about throttle position. When I was testing the jetting I was just pulling hard through the gear WOT to find my correct main and needle.

I worked from Main setting, to Needle setting to Pilot. Like I mentioned, I've been fairly certain I am lean on the pilot. and cruising in 5th gear at 83MPH at approx 5000RPM I am NOT wot.

The rarely take the highway, however I need to get this sorted as I plan taking some long journeys soon that will require boring slab time.

I don't guess you have any dynos in yoru area that you can do an air/fuel peak tq runs to find out if you are getting the fuel you need?

The pilot jet affects all the circuits. If you are running fine in another circuit and lean in others adding a bigger pilot will make the one rich and the others better. But anyways without a sniffer and a dyno its hard to know which way to go..

 

[TheCafeKid]

Thanks for the response. I am familiar with plug/throttle chops. Kinda lost sight / forgot about how it's really all about throttle position. When I was testing the jetting I was just pulling hard through the gear WOT to find my correct main and needle.

I worked from Main setting, to Needle setting to Pilot. Like I mentioned, I've been fairly certain I am lean on the pilot. and cruising in 5th gear at 83MPH at approx 5000RPM I am NOT wot.

The rarely take the highway, however I need to get this sorted as I plan taking some long journeys soon that will require boring slab time.

Josh, just for kicks, check what size your pilot air jet is before you change your pilot fuel jets. If they're unlike mine they'll have either 160s or 170s in them. I too have been putting of the 47.5s but only because i think that my pilot air jets are too large. I think i have 180s in mine, and I also think that if i go to a smaller size, i will get rid of popping without changing the pilot fuel jets. The bonus to this is, you can change the pilot air jets without removing the carbs In case you didnt know, the pilot air jets (or Air correction jets as they are sometimes called) are the jets on the pod side of your carbs. They are recessed, but still slotted and can be removed. if you do it with the carbs in, you'll need a dental pick or something to grab them with once you unscrew em. Take a look at the size of yours, and let me know what size they are. I am trying a little experiment. If you dont have a set of smaller pilot airs, the ones that came with the DJ kit math out to mikuni 150s, and that SHOULD help...

 

[TheCafeKid]

I don't guess you have any dynos in yoru area that you can do an air/fuel peak tq runs to find out if you are getting the fuel you need?

The pilot jet affects all the circuits. If you are running fine in another circuit and lean in others adding a bigger pilot will make the one rich and the others better. But anyways without a sniffer and a dyno its hard to know which way to go..

Larger than necessary mains will cause more problems than they'll solve. ive already fought this issue. By having a too large pilot, you have to lean the needle out to compensate so you dont have bog in the upper needle section. When you do that, you then have to richen the pilot in order to compensate for a leaner pilot/needle transition. Things just compound from there, and then you end up with a rich, stinky bike that may feel quick, but not nearly as soo when you compare to a properly tuned bike. I trust that you're a drag racer, and have lots of experience jetting, but what works at the track, taking off from WOT doesnt necessarily translate to the street where you seldom see WOT. Which is why the 'experts' (and im certainly NOT one of them) suggest that when tuning CV carbs, they should be tuned from the MAIN jet down, rather than the other way around like radial slides, or other mechanical designs...

 

[maro]

Larger than necessary mains will cause more problems than they'll solve. ive already fought this issue. By having a too large pilot, you have to lean the needle out to compensate so you dont have bog in the upper needle section. When you do that, you then have to richen the pilot in order to compensate for a leaner pilot/needle transition. Things just compound from there, and then you end up with a rich, stinky bike that may feel quick, but not nearly as soo when you compare to a properly tuned bike. I trust that you're a drag racer, and have lots of experience jetting, but what works at the track, taking off from WOT doesnt necessarily translate to the street where you seldom see WOT. Which is why the 'experts' (and im certainly NOT one of them) suggest that when tuning CV carbs, they should be tuned from the MAIN jet down, rather than the other way around like radial slides, or other mechanical designs...

I'm guessing you meant to say Main there. Anyway, you and I had this convo as well.. TRUTH BE TOLD.. I have a sneaking suspicion that I really am one size too large on the main and that what you are describing here is what is really going on. HOWEVER.. it's so close right now, that I would rather just go up one on the pilot to avoid spending another month pulling the carbs out (I have stock airbox) and jetting over and over again just to realize I was correct on the main all along.

maybe in the fall I'll play again, right now I just want to ride somewhat smooth, if I lack a bit of power, well, I've never ridden another 1100 so I don't know the difference....

I am getting 47 miles to the gallon so I am def lean somewhere......for now we'll say the pilot and I'll just adjust that.

FYI - I like that whole air screw suggestion. There is def an air screw on the CV BS34's?. I'll have to look into that.

 

[TheCafeKid]

I'm guessing you meant to say Main there. Anyway, you and I had this convo as well.. TRUTH BE TOLD.. I have a sneaking suspicion that I really am one size too large on the main and that what you are describing here is what is really going on. HOWEVER.. it's so close right now, that I would rather just go up one on the pilot to avoid spending another month pulling the carbs out (I have stock airbox) and jetting over and over again just to realize I was correct on the main all along.

maybe in the fall I'll play again, right now I just want to ride somewhat smooth, if I lack a bit of power, well, I've never ridden another 1100 so I don't know the difference....

I am getting 47 miles to the gallon so I am def lean somewhere......for now we'll say the pilot and I'll just adjust that.

FYI - I like that whole air screw suggestion. There is def an air screw on the CV BS34's?. I'll have to look into that.

its not an air SCREW its the Pilot Air Jet...if you were to look at the carbs on the intake side, the fat side of them, you will see a jet about the same size as the main jet. thats the pilot air jet, or air corrector. On the two sets of carbs I have for my 82 1100 and my 83 1100, they are both a 180 i believe. Supposedly, the STOCK size is a 160?? If thats the case, then, in the process of both of the POs attempts to rejet these bikes for pods, they'd changed out the pilot air jet to a larger size. This will LEAN out the pilot circuit, thus making it harder for you to be able to dial the pilot circuit in with the STOCK pilot jet, as DynoJet says you should be able to. Its also the likely cause of the decel popping that I cant seem to get rid of all the way, and *Im* all the way out on my pilot screws. This actually sucks at idle because the bike wants to hang for a while when i stop because its simply getting too much fuel. But if i back the screws down, it pops like a son of a gun. I am waiting on a new set of Orings for the carbs that were just cleaned and re-shot nice shiney black. So what *I* plan to do is use the Dynojet air correction jets, which are about 150s, give or take, in conjunction with the stock pilot jet. Im good everywhere else in the jetting so if what Im planning to do works, I will let you know, and you can give it a shot on your bike. I think reducing the pilot air jet size, or at least making it stock, will help smooth the pilot circuit out, as well. Do me a favour when you think about it, and see if you can get the size of your pilot air jets and let me know. Im curious to see what size yours are to see if the info i have on their stock size is wrong, or to see if changing the air jets was a common practice.

 

[maro]

I bought my carbs from chef, so I can ask him. But I'll take a looksy this week just to be sure.