freshly rebuilt motor but hearing popping sound?

[Beefcake]

Hi all, I just rebuilt the motor on my tomberline crossfire and everything actually worked out. I didn't even take out the passenger seat . Well the stock air box was broke when I bought it and I replaced it with a black uni filter (2 1/16'') connected to a 5'' rubber sink coupler for an intake. The motor runs great after the rebuild but I'm hearing a popping sound at WOT. I didn't change the main jet yet for the carb so I know its leaning out a little bit. I drove the motor @ low RPM's for 5 hours to break it in before going WOT. Any help would be greatly appreciated. Also what jet size do you guys recommend for that size uni?

[SYCARMS]

You will also need to open up the exhaust since you are getting more air the exhaust also needs to flow more, than rejet with about a 122-125 jet. Your popping could be the lean mixture at wot. TOM

[olderthan]

open your exhaust
you will need to rejet
what is your location/elevation

[BuggyMaster]

my vote is running lean. That can cause that popping.

[Beefcake]

I am right at sea level well I'm not sure, I can see the ocean from my house but its maybe 3 miles away.

[olderthan]

i would start around 125
after opening exhaust
you may end at 127.5 or 130

[chuckorlando]

Dont run it at wot till you fix the jets. Get 4 or 5 sizes so you dont have to re-order.

[Beefcake]

When you say open up the exhaust, could I cut the tip off and pull out the fiberglass packing and just re weld it? Or do I need a new bigger header pipe too?

[BuggyMaster]

They mean get a better flowing exhaust. be it gutting yours or buying a performance exhaust.

[SYCARMS]

Here is what I do, it works well with a stock motor. If later on you decide to go with a big bore and cam you will need to replace the exhaust system, but until then this works fine. You will need a hack saw,1" hole saw, 3/4" wooden dowl, 2" length of 1 1/4 od pipe/conduit, and access to a welder.
First cut the tail pipe as close to muffler as possible. next cut a piece if 3/4" wooden dowl and drive in remaining tail pipe this is used in order for hole saw to make pilot hole. Now with the hole saw drill out that tail pipe completely. Once drilled out lightly tap in your 1 1/4" od pipe than weld. This will increase the flow of exhaust and sound pretty good without increasing noise level much. The wooden dowel can be purchased at any hardware or lowes. If you know an electrician you can get some scrap ends of conduit. Any thin walled pipe will work once you have this in place if you don't have or know anyone with a welder than take it to the local muffler shop and have them weld it. TOM

[Beefcake]

So what your basically saying is that all I have to do is make the very tip of the exhaust bigger (to 1 1/4'')? I have access to a welder, hack saw and the wooden dowels. What I'm asking is couldn't I just use a step drill to make the exhaust hole 1 1/4'' after cutting the tip off? I was under the impression I'd have to pull all the fiberglass packing out of the muffler.
I don't have a hole saw but I do have a step drill bit that goes to 1 1/4''.

[SYCARMS]

Step drill will work fine. As far as I know the Chinese buggy stock exhaust does not use fibreglass in their mufflers except for the performance mufflers, crossfire included. What is inside are baffles, and removing them will make the engine grossly loud and you will not have the required spark arrester required in many state and federal lands. The exhaust is choked down by the tiny tail pipe and therefore by increasing its size will remove considerable restriction. The engine does require some restriction in order to help scavenge the burned gasses from the engine. As far as going back with a larger tail pipe as to just enlarging the hole, this will produce a better muffler tone. Until you go with the more major engine mods your muffler modded in this fashion will help the engines performance. When and if you get to the point of modding the engine with a big bore kit or port and polish with or without a cam you will than need to upgrade to a performance exhaust system. TOM

[Beefcake]

Thanks for all the help! SYC I'm gonna do the method you told me tomorrow. I was also wondering if there was a performance exhaust for the GY6 other than that Hammerhead exhaust. I don't want to spend more than $150 if its doable. I am planning on doing the 175cc big bore and stroker crank in the future but my piston rings are only a week or two old.

[SYCARMS]

There is not much available in performance exhausts. The old Eastside exhaust which by the way is no longer available,will not fit the Tomberline, same problem with the MRP which is a copy of the Eastside exhaust. This leaves you with the Hammerhead. The FMF slip on 2 cycle muffler would cost you between $120.00 - $130.00 but you will have the same pipe which with a 170BB would also need replacement. I started carrying the TK exhaust which retail for $280.00 but I have to research weather it will fit the crossfire. What ever you do when you decide to do your big bore unless it is the 59mm kit which is a drop in kit do not go for the 61mm drop in for the bottom of the sleve has been shaved to fit the case and will not be very long lived. Get the block bored it only costs $75.00 and you will deffinately have a much more longer living and reliable engine using the thicker sleve. TOM

[Beefcake]

If I were to get the block bored myself, how many mm's could I go if I had the crankcase bored to match? I know a guy whos taking CNC maching classes and could take it in as a project and do it for free. I guess I'll have to bore it to where I can buy a piston and rings for it. I could also probably get him to make me a custom header pipe to weld the slip on muffler to. Do you know the part # for the FMF slip on or maybe have a link? I've tried searching using various 2 stroke dirt bikes and all its giving me is $300+ exhaust systems. Also for the custom header pipe, how much bigger would you recommend? and if there is a better angle to run it, or run it just like stock just bigger circumference? Keep in mind I do plan on getting a no rev cdi in the near future, probably before the big bore kit.

[SYCARMS]

You would bore the case to accept a 62mm cylinder. Just make sure whoever bores it knows what they are doing cause if they mess up than it is replace the case or engine. Don't try to cut corners and go the cheap route. Research what works and what doesnot work And just because some one went the easy cheap rout and it worked for several months does not mean it works. What works has been done for years with out any bad effects.Remember all the dealers ,supliers and factories are trying to make money (your Money). There are many inferior parts sold to suppliers than to dealers and finally on to customers all on the factories word. s#%t runs downhill and you are at the bottom of the hill. I can think of at least 4 people right now who went the cheapest route building a performance motor cheaply and with all the money and time they have invested they could of had me build them 2 complete ass kicking motors for the same money they had in total investment and be driving their buggies. As far as the exhaust again trying to cut corners does not pay off. If you want performance than purchase an exhaust system that has been engineered for performance, unless you have access to the $7000.00 Dyno and countless hours tweaking and testing just invest in one proven to do the job.For the mods you are doing opening up the exhaust will do just fine. If you want the FMF slip on give me a call and I can get one for you. Building a performance engine is no cheap task no matter how you look at it.Decide on what your budget will let you do and save. Remember we are all out here to make money your money some make their money honestly and some don't. Everybody wants to get the best deal but the cheapest deal is many times not the best deal in the long run. For example if you research the performance exhausts for atv's you will find they cost in the area of $300.00 up to $700.00. You are paying not only for the materials used but also for the research and development some educated person with experiancehas invested. There was available at one time the eastside exhaust which was $300.00 plus. This made a huge performance improvement, than someone sent one to China to copy and the result was although $100.00 cheaper did not perform 1/2 as well, did not fit properly and did not last as long. Waste of money in my opinion.Educate yourself and buy smart cause as PT Barnum once said there is a sucker born every minute. TOM

[chuckorlando]

Agreed. If your paying retail you should expect to have up wards of 1600 in a fully built gy6 and still have room to spend. I know cause I've done it. Tom Syc built my First motor for me. Over a year of hard riding and she still runs strong today. Tom Syc has the fastest 250 at the drags and my 150 runs less than 1sec slower. His 150 is even faster.

Tom is wrong on one small fact. A custom exhaust from a real exhaust guru will run 800+. An off the shelf one from the same guy's will run 300+. A custom exhaust is tuned at each rpm level and can take alot of time. You can make a header but it wont be the real deal. If you do make a header then step it from a hair larger than stock or even stock. Then up the pipe to what you need.

If your in a performance mood one of Toms ported heads and cam will give you more gains than a bb kit. If you are gonna split the case for machine work then a stroker is a no brainer.

[Beefcake]

I was able to get the exhaust opening to 1'' and I opted out for the pipe I just left the hole