Jetting question

[SRosaJr]

I understand the principles of carb jetting, but here's my issue...I have a yerfdog with a Howit 150cc engine, bone stock with only a Hammerhead Performance exhaust and Unifilter intake kit, a orange HP CDI and coil upgrade and a new standard NGK copper plug, my question is why when I jet it at 130 does it bog out really bad, but runs fine on a 108 jet? Its starts fine, runs up thru the rpm range fine, and hits the upper rpms fine, does not hang and comes back to an idle just like it should, now this is all done in my shop while up on jack stands with no load other than spinning the drivetrain. Right now I'm also repairing the front suspension because the previous owner hit something with the right side suspension assembly and there are a few tweaked components, it can be driven but it turns like a garbage barge to the left, turning right is not a problem. Will it act differently once there is s load put on the engine?

[neo71665]

Sounds like the 130 is too big of a jet.

Jetting isn't as cut and dry as you have XXXX and XXXX parts so you have to have a size XXX jet. You have to tune and jet according to the engine you have and elevation you are at. Get a jet kit, run it, read the sparkplug, and adjust according. I'd suggest starting with the 108 and going up till the plug reads too rich, then drop back down one size.

[SRosaJr]

I assumed with the intake and exhaust that it would be around a 130, since most of the buggies with the same setup are running a 130ish jet, but the 130 seems way overjetted...I need to get me a jet kit, and my steering repaired so I can take it for a test ride as it sits right now left turns are not happening...

[neo71665]

I have a bore kit, 28mm carb, intake, a custom exhaust, and only running a 120 jet. You go by the armchair web worriers I should be running way bigger. What they have to say might get you started but at the end of the day you can only do what the engine wants.


Do your own tuning to what your engine needs, not what somebody across the country is running. Get on ebay and buy a jet kit, when I got mine I think a 10 piece was like $6 but last time I heard they have went up. Learn to read your plug, tune to what the engine needs/wants.

[plee911]

NEO is right

If you don't mind waiting for jets there are some nice kits that come with 10 main and 10 pilot jets on ebay.

The price for mine was about $10 and well worth it.
Took a month to get here but when everywhere I looked stateside wanted between $3 and $5 per jet I couldn't argue with the price.

When buying look at the pics and look for jets that are clearly marked for sizing in the pics.

You will find cheaper options but the jets will have crappy markings making them a pain to work with.

The only way to figure out what jets you need is to pick a starting point and read you plug.

There area few tell tell signs like backfire on deceleration that will warn you that you are lean.

There is no substitute for reading the plug.
Run her to full throttle and hold her there for about a minute and kill the engine with the throttle still wide open. Don't let her come back to idle or idle down during the shut off this will give you a clean read on the plug.

From what you posted if it was stock with a 108 I would not have made the jump clear to a 130.

Maybe go 110 see how she runs and check the plug if still lean go to 115 if she is rich your target area will be between the 2 sizes to get her perfect.

Remember a little rich is always better than a little lean.

[SRosaJr]

I'm going to look up the jet kits, Amazon has them and the price isn't too bad and I have prime which is 2 day shipping! I'm going to run a comp test on the engine, she has seen some use, no smoke, no weird noises but I just want to check here out first before I get too happy spending money in the wrong places...my list prices out to just under $800 for what I wanna do, that's not doing anything to the engine but what's already done.

[OLDKID]

Tuning on jack stands / No Load ???
I think you're literally SPINNING YOUR WHEELS !

[SRosaJr]

That's why I asked about the no load thing, I have a trail thru the property I have but the way this thing steers I would spend a majority of my time pushing it out of the scrub on the sides of the trail, I guess you cant get an idea how it will run with the wheels off the ground? Ill have to get the steering issue sorted out first before moving forward with any type of test and tune...

[plee911]

Steering isn't a huge concern since you don't want to be turning anyway. You need about a 300 to 400 ft strait run with throttle wide open the whole way. kill engine at the end with throttle wide open. Then pull and read plug