Here we got with yet another fueling question. I'm gonna be an expert on carbs if I ever get this thing running right.
1999 Monster 750, OEM Mikuni carbs, almost new (maybe 1500 miles on them) emulsification tubes, 35,000 miles.
Settings: Stock mains & pilot, needles shimmed about 1mm richer, air screw about 5 turns out on both carbs. Does the same thing at 5.5 turns out. At 3 turns out, I get a stutter at low RPMs when I whack the throttle open, seems to be a lean issue as it gets worse at 2 turns out. Idles better at 2 and 3 turns out though. Pulls like a maniac once off the pilot circuit, as in power wheelies with a slight bump in the road in 1st gear.
The Idle hunts, as in sounds normal and then slows down and sounds labored, comes back up and goes back to the slow labored sound. No real pattern in how long it sounds normal or goes form normal to slow & labored.
Where to start?
JM
Mine too. [thumbsdown]
But I have just started looking into it.
2007 695
When I start it, choke is on it wil jump up to 3k rpm back down to 2k then up again.
easy stuff first, check for vacuum leaks and sink throttles.
I have done a sync, and I've got new diaphragms. All the vacuum tubing seems good too from visual inspection.
I've got some new plugs, I'll toss those in and see what happens.
JM
What is your warm idle speed set at?
No tach, so I have no idea.
JM
Try raising the idle a bit and see if it helps.
The screw is a fuel screw, and 5 turns is pretty far. I'd go in to 4 turns.
Keep in mind that needle position affects pretty much all ranges on those carbs, and they came form the factory really lean. If your needle has adjustment grooves I'd drop the clip another notch (raises needle) and try it.
A jet kit would help that bike.
I was thinking I was a bit far out and should go up a size on the pilot. No notches, but I've added a shim under the OEM washer, I could easily add another, but it does run REALLY good once you get off the pilot circuit. I'll run the fuel screw in a turn and see if I get any lean missing.
I'll turn the idle up a little and see too.
JM
Quote from: the_Journeyman on August 07, 2011, 11:43:40 AM
I was thinking I was a bit far out and should go up a size on the pilot. No notches, but I've added a shim under the OEM washer, I could easily add another, but it does run REALLY good once you get off the pilot circuit. I'll run the fuel screw in a turn and see if I get any lean missing.
I'll turn the idle up a little and see too.
JM
I have a set of stock needles with adjustment grooves from a 900.
Wanna try them if you don't get it sorted?
I may if fiddling with the idle & moving the screws back to 4 doesn't get me anywhere.
JM
Seems I have two options. Hunting or hanging idle. When I bring the speed up where it sounds about right, it hangs a few hundred RPM high once I blip the throttle. When it's down when it doesn't hang, it does the hunt/sound labored thing.
1) Could I have shimmed the needle TOO high?
2) I'm also burning oil it seems, would blow-by make tuning impossible?
Why can't this be simple? I've got a riding trip next week!
JM
The needle doesn't affect idle. Idle mixture screws, main and pilot jets will though, as well as float level. How are the spark plugs?
Can't remember when I put new ones in last. I have a set I got last week I'll toss those in. Here's what one of them currently looks like:
(http://i304.photobucket.com/albums/nn168/the_journeyman/Molly/DSC_0081-1024.jpg)
Gotta love a good macro lens!!!
JM
I've battled this problem for years and on my bike it came down to a gasket leak were the intake manifold meets the head. Here is how I found the problem. On a tip from my local auto parts store I sprayed carb cleaner at all of the connections on the intake system downstream of the carbs themselves. The engine revved higher when it was sucking in the carb cleaner through the leak.
Plugs have some deposits. If rich enough at idle you wash a little oil off the bore and add oil deposits to rich fuel deposits. How bad is the oil usage?
Normally idle will hang when lean, but an overly rich idle mixture with a high idle speed to compenxate can cause another type of 'hanging' also.
How are your float levels? Hope they are ok. 14mm is correct from memory.
Turn down the idle speed so it just idles and adjust for the fastest and strongest, most even sounding idle speed with the idle mixture screws on fresh plugs. Set your speed after that as you may have it too high to compensate for rough running, but you want to hear the idle clearly speed up when you turn those screws in the right direction.
Let us know how you go.
Ok, new plugs are going in as soon as I figure out what the gap is to check the new plugs.
JM
Fresh plugs and it idles much better. I'm going to check plug color and see if it indicates rich or lean.
JM
Idle is good, actually responds to fuel screws. I went in a half turn and got a slightly faster idle. Seemed to run ok & idle ok. Back to fussing with the needle shims. If feels a little lazy in the midrange.
I'm amazed at the difference new plugs made.
Plug deposits are very white, so I'm going to add an additional shim under the needle and see what happens.
JM
After trying a few different things, I wound up nearly tripling the needle height from OEM. Currently at 3.5 turns out on the air screws, might go back to 4 though. I'm thinking the main needs go be larger too. I do have BCM filter & Termi pipes, so that makes the factory lean settings probably more noticeable and harder to tune without adding a jet kit.
So, here's where I wound up:
1. Full throttle is weak, as you roll off, the bike pulls better. I think that means lean.
2. It pulls strong and smooth in mid-throttle & RPM with reasonably crisp (Not quite FI crisp) response.
3. It is idling steady, but I get a lot of popping when I decelerate with a closed throttle.
Plugs still indicate lean, but it's running much better.
Starts easier too, probably the new plugs help with that.
Quote from: the_Journeyman on August 09, 2011, 12:38:01 PM
After trying a few different things, I wound up nearly tripling the needle height from OEM. Currently at 3.5 turns out on the air screws, might go back to 4 though. I'm thinking the main needs go be larger too. I do have BCM filter & Termi pipes, so that makes the factory lean settings probably more noticeable and harder to tune without adding a jet kit.
So, here's where I wound up:
1. Full throttle is weak, as you roll off, the bike pulls better. I think that means lean.
2. It pulls strong and smooth in mid-throttle & RPM with reasonably crisp (Not quite FI crisp) response.
3. It is idling steady, but I get a lot of popping when I decelerate with a closed throttle.
Plugs still indicate lean, but it's running much better.
Starts easier too, probably the new plugs help with that.
Your jetting is getting a little disorganized. I'd suggest that first check for leaks in the intake as I suggested earlier.
Also check for leaks in the exhaust. Leaks at either intake or exhaust can cause lean running and are problems you will never solve with jetting. Your symptoms at idle sound more like a leak issue than a jetting one.
If you have no leaks and your bike still has problems as described start by solving the WOT problem first by changing the main jet. Get WOT sorted first! Your symptoms sound like a rich mixture to me. In my experience a lean mixture results in hesitation or popping.
After that, if you have problems with partial throttle openings adjust the needle.
Adjust ideal mixture last by adjusting you air screws.
Also you could use an AFX air-fuel Monitor http://www.ngk.com/afx/ (http://www.ngk.com/afx/) to help you sort out your problems if you have no leaks.
It wouldn't hurt to check for manifold leaks as AKMNSTR suggested.
It's good you are considering a Factory Pro or Dynojet jet kit with that high flowing filter and pipes. It will give you a tuning range you dont have at present. If you can get main jets cheap enough you could try DPs needles. There is such a minor taper on the stock needle that shimming it has less effect than you would hope for.
I have seen decel popping from manifold air leaks, too much (rich) fuel burning in the exhausts and also from too lean a setting, so try half a turn out on the IMS and see what happens.
Sounds like you are learning heaps and making progress. I like how you picked up on the main jet being lean. ( I have seen similar WOT symptoms with too rich), but your plugs are white and you have a freer filter and pipes. It's great you are reading your plugs too.
Us older guys brought up on carbed bikes all went through this.
Full throttle is a main jet issue. Rich or lean can difficult to determine with the butt dyno, but too rich short of stupid rich is smooth but may have noticeable power loss. Lean usually results in ridability problems.
Lets not forget this is stock jetting.
I doubt any part is rich.
Quote from: howie on August 09, 2011, 08:10:38 PM
Full throttle is a main jet issue. Rich or lean can difficult to determine with the butt dyno, but too rich short of stupid rich is smooth but may have noticeable power loss. Lean usually results in ridability problems.
All true. The main jet also influences all of the other settings and is why I suggested sorting it before other adjustments.
QuoteIt's good you are considering a Factory Pro or Dynojet jet kit with that high flowing filter and pipes.
Maybe the best advice given here. The kits suggest jettings that have been worked up for your engine setup. I didn't realize earlier that you are working with carbs with the stock jetting.
Quote from: akmnstr on August 10, 2011, 05:49:19 AM
All true. The main jet also influences all of the other settings and is why I suggested sorting it before other adjustments.
Maybe the best advice given here. The kits suggest jettings that have been worked up for your engine setup. I didn't realize earlier that you are working with carbs with the stock jetting.
Absolutely!
Got back from a riding vacation last night. Here's my observations. It's obvious I need a jet kit, that'll come in this winter when I have time to disassemble the carbs again.
In the mean time, here's how things run.
Bottom end through mid throttle is great. Very strong pull from idle.
Top end is in bad shape. Chasing down some of the fast guys required a couple seconds of WOT. This resulted in a NASTY forward surge as I closed the throttle. Likely a lean surge I'm guessing.
JM