Main Jet Question

[Les]

I have a 92 Kitty Cat that works good when it is cold outside (-15C) but it turns into a dog when it gets warmer out. It will work well for about 10 mins and if he stops moving, the sled just sits and bogs. If I pick up the rear of the sled and clear it out, and give him a little push, it will work good for him as long as he does not stop moving
I have disassembled and cleaned everything in the carb, checked compression (new pistons and rings), new plug and it is still behaving the same.
I thought I would try a smaller main jet. It has the factory 72.5 main jet and I thought I would try the 70. The only place around me that I could find this has a #70 but the head on it is a little larger (fatter). When you stand them up on the counter, they are the same length, etc.. but the round head is larger. There is enough clearance in the bowl to fit so I took it.
My question is.... does it matter if the jet head is slightly larger? Does anyone have any other suggestions?
Les

[dantheman]

before you do all that did you try a hotter plug????? otherwise you can lead the jet in with solder and re drill it if you have a set of jet drills

dan

[Guest]

before you do all that did you try a hotter plug????? otherwise you can lead the jet in with solder and re drill it if you have a set of jet drills

dan

I think I have the stock plug that was specified (NGK BR6HS). Do you think a hotter plug would do the trick? Is there anything to watch for when running a hotter plug?

[dantheman]

if you run a hotter plug it will take care of a minor condition of beeing rich,
first of all what oil are you using, what ratio are you mixing it?? im not sure you can get a hotter plug, but what ya wanna watch for is after running it wide open for 10 20 seconds , kill it and take the plug out
look at it it needs to be a redish brown color, not black as it should look at the moment from what you are describing, second make sure its not a really really light shade or white or you could be in trouble,
best way is measure the exhaust temperature, but you need a special setup for that.
I personally from what you are desribing would lessen the amount of oil beeing mixed.

dan


Example NGK codes:
[P] [6] [E] [S]
[D] [8] [E] [S] [-] [L]

Field one: Thread Diameter A 18 mm
B 14 mm
C 10 mm
D 12 mm


Field two: Construction C Hex size 5/8"
K Hex size 5/8" with projected tip (ISO)
M Compact type
P Projected insulator type
R Resistor
SD Surface discharge for rotary engines
U semi-surface discharge
Z inductive suppressor


Field three: Heat Range 2 Hottest
10 Coldest


Field four: Thread reach E 19 mm
F tapered seat
H 12.7 mm (1.5")
L 11.2 mm (7/16")
If this is blank, an 18 mm diameter plug has 12 mm reach; and a 14 mm plug has 9.5 mm (3/8") reach.


Field five: Firing and construction A,B Special design (no details given)
C special ground electrode
G Racing use
GV Racing V-type
H Half thread
K 2 ground electrodes
L Half heat range
LM Compact lawn mower type
M 2 ground electrode for Mazda rotary engine
N Special ground electrode
P Platinum tip (premium)
Q 4 ground electrodes
R Delta ground electrode for BMW
S Standard 2.6 mm electrode
T 3 ground electrodes
V Fine-wire electrode, gold-palladium
VX Platinum tip (high performance)
W Tungsten electrode
X Booster gap
Y V-groove center electrode


Field six(after the dash): Wide gap 8 .032"
9 .036"
10 .040"
11 .044"
13 .050"
14 .055"
15 .060"
20 .080"
L Half heat range
N Special ground electrode (note: appears to be limited to BMWs)

[Les]

I am mixing 50:1 with a synthetic oil. Even after a new plug and him running around wide open for 5-10 mins, the plug is black. I will try the test you mention below to see how it looks.
For such a simple engine, this one has really been a pain in my butt!
Les

[Guest]

I went to a leaner jet size and it isnt as sluggish as it was with the Stock Jet I think I have a #70 in it now. They are pretty "Fat" from the factory

[Milf Hunter]

Check with Steve at obups he can tell you what to put it in.

[Les]

I think the leaner jet should help. I went onto obups and found the jets but by the time I pay for shipping and exchange (I'm in Canada), the $5.00 jet got pretty expensive.
From what I can tell, I need a Mikuni 102/221 #70 and all anyone around here can get is a 100/604 #70 which has a slightly larger head. Does it matter if the head of the jet is larger than the stock one?
I guess I'll just try it out and watch the plug.

[Jonn]

Hi Les. My name is Jonn and I'm from obups.

These carbs are definately sensitive and can sometimes be frustrating to deal with. I completely understand your pain! With such small passages in the carb, they can sometimes be almost impossible to completely clean. In our 25 years of working on these Kitty Cats we've had a few that just couldn't be fixed.

Obviously with the price of a new carb being expensive, I recommend you exhaust other cheaper options first. The jet is definately a place to start. Typically folks go to a #70 main jet and find this helps considerably. Some will install a 67.5 main jet to get even better performance but then you border on being too lean. If you choose to install a 67.5, you'll want to check the plug in cold weather to make sure it's not too lean.

You've seen the price of $5 on our website and I know the standard shipping that gets applied (FedEx / UPS) is pretty high to send such a small part. If you had called me I would have charged you the $5 plus .37 for a stamp and mailed it USPS. Call or email me if you want to do that and get the right jet(s) for your carb.

As for the spark plug, you should stick with one of a couple choices. Stock is BR6HS which is fine but doesn't fire as well because it's a resister plug. For racers we recommend using a BP6HS. This plug is a non-resister and has a longer electode (projected) which provides a better spark without increasing the motor temp. If the Kitty Cat is driven around the house and is messing up the TV, you can compromise and use a BRP6HS (resister and projected).

I hope this information was helpful, and good luck with your Kitty. Let me know if I can be of further help.

[Les]

Thanks Jonn. I am going to try it out this weekend (don't have snow yet but the grass will do) and see how it goes. You may be getting a call from me next week if the jet I have doesn't do the trick.

[Bill Tripp]

Les,

Your problem I feel stems from a fuel evaporation problem...See it alot in racing kitty cats....Because gas is so junky at the gas stations it will cause your sled to bog as it heats up making you scratch your head wondering if it is lean or running rich...Your crankcase is heating up and the piston dome is getting very hot.....I take it you have the governor ty-wrapped??? You mentioned that very thing is oily...As the fuel charge enters the cylinder everything is so hot that the fuel evaporates and goes right out the exhaust port and just leaves the oil.....VP makes a good pump gas called MS93 and another alt. is Shell 93 V-Power.....done alot of dyno testing and this is the best fuel for stock engines at WOT for any long period of time. May want to increase your mixture to at least 40:1.. Change your plug to a BP7HIX NGK....it's a iridium plug and takes 4000 less volts to fire under high cyl. pressure....70 mj is fine....Float level is also very important....plus you may want to change your needle and seat to a 2.0 from the 1.5....that will also help.....Bernie Cozad at Fox Dist has them 630-513-9700....maybe Wahl bros racing might have them....Check out my web site......Http://www.kidsperforamnce.net Hope this helps

[Bill Tripp]

I mispelled my website.....dont visitwww.kidsperformance.net

[Jonn]

I also have the 2.0 needle & seat in stock.