well, a mic would be best, otherwise you're just guessing. As far as the stroke, yes thats exactly what you do. On some engines (somewhat rare) the piston will actually somewhat come out of the bore, so you'll have to take that into account as well, and some pistons are domed. I'm not exactly sure how that is measured, I'll try to do a lil research and let you know.

 

Thanks allot for the info, but I don't know if I am going to do it or not. According to the manual, I will have to pull the engine out of the frame to pull the head off. The engine run's really good and I sure hate to open it up. I'm afraid if I pull the engine out, then I will open a whole other can of worms[img]i/expressions/face-icon-small-happy.gif[/img] Rounded, striped or broken bolts and who know what else. I usually start with good intentions to check something on a perfectly good motor, and wind up screwing something up and costing myself a whole lot more money and hart ach. Since the engine seam’s to be in really good shape, I think that I will play it safe and leave it that way[img]i/expressions/face-icon-small-happy.gif[/img] I'll just try fixing the real problem for now instead of creating more[img]i/expressions/face-icon-small-blush.gif[/img] If you have any info on how to correctly jet a carb that would be greatly appreciated. I think that I am going to get the 36mm Mikuni carb from Powroll. Do you know anything about this carb? Is it better than the Keihin PE carb that I pulled of my 350x? I know that you said that it was out dated, which I'm sure it is considering that it was put on there over 12 years ago.

Thanks,
Brian

 

I was told by powroll the only difference I would see with their carb was more top end power.They also told me to go 3 sizes up on jetting (make it richer)to give the built engine enough fuel with the stock carb.

 

Hi Truck, I bet you can’t wait to get that baby running[img]i/expressions/face-icon-small-happy.gif[/img] I just spoke with Powroll, and described my situation to them. They told me that they did indeed use to offer a 496cc kit for racing and that is probably what I have. I am waiting to speak with someone there that can really give some info about it. I think that I am going to use their carb kit as it seam’s to be the only one that I can find that comes with a complete throttle cable and twist throttle, which is what I need. My throttle cable is toast, and a stock one will not work, that is how I got into this situation in the first place[img]i/expressions/face-icon-small-blush.gif[/img] I hope that it won’t be a pain to get it jetted right. How are you planning on running your air box? This maybe a perfect time for me to open mine up, and run richer jetting in the new carb for more power. Where did you get your 4 wheeler conversion for your 350x? Is there a web site that I can check out?

Thanks,
Brian

 

I am not doing any air box mods,I ride all year in mud,rain,snow,dust & just don't need anything even trying to get in my engine.The 4 wheeler conversion is from Hi Performance Machine 619-448-8802 they will send you a catalog for free.They are shipping out my kit tomorrow.Good luck with the carb.It takes them about 6 weeks to get a kit to you.I will be putting mine together within the next 2 weeks so if you wait I will post before & after pics Here & the honda forum.

 

Hi Dill, well, I talked with Powroll and they recommend like you to pull the head and measure it to see exactly what I have. They made a good point in that I need to know what engine it is, for valve adjustments and other tune up spec.'s. They told me that if I take it apart, measure it, and give them numbers off the cam and such that they can tell me exactly what I have. Great service over at Powroll, and I haven't even bought anything from them yet. I know who I will be doing business with from now on[img]i/expressions/face-icon-small-smile.gif[/img] Thanks for all your help, and wish me luck, hopefully I won’t screw anything up[img]i/expressions/face-icon-small-wink.gif[/img] Oh, they also offer a FCR carb like you mentioned and suggested that I try that. But they wanted me to check to see what size engine I had before I ordered that because they said that if it was only a 368cc, that I would really see that much of a difference, versus if it was a 496cc.

Thanks again,
Brian

 

cool..let us know what you find.

 

Well, after taking the engine out of the frame, and pulling the head off, along with all the other disassembly work required to check the engine size, I discovered that I have a stock 350cc engine! Can you believe that [img]i/expressions/face-icon-small-blush.gif[/img] I can't believe that people will lie like that for no reason. I wasn't buying the 350x because I thought that it was a Big Bore, I just wanted a 350x [img]i/expressions/face-icon-small-mad.gif[/img] Oh well, at least I now know exactly what engine I have.

Now that I have the thing completely torn down, I decided to just go ahead and rebuild the engine, so that I will know exactly what I have, displacement wise, as well as engine condition. I ordered Powroll's smallest Big Bore kit, the 368cc kit with 10:1 compression piston, rings, piston pin, Mid Range cam, valve springs, and gaskets. I also ordered new rocker arms, Cam chain, valves and a 3-angle valve job. A new SuperTrapp exhaust system, and Carb. I ordered a stock 300EX carb from Honda, which was recommended by Powroll for this kit. This carb according to Honda is a 32mm oval venturi Keihin. Powroll, said that it is actually measured out at 29mm, but it is a good carb and it has an accelerator pump, "Pumper" They said that it is the same size as the carb that came on the 350x, but that it is better because it is a pumper and a better design. My manual says that the stock carb was a 31mm venturi carb, but I guess everyone measures carbs slightly differently. This sounds really small to me! Do you guy's think that this will be a mistake? How about you Truck? Like you, they told me that I would only loose about a 1/2 mph off the top end, but would gain good throttle response, and low and midrange power? They said that most people way over-carb there engines. Do you guys agree with this? Did I make a mistake buy ordering this carb? What would you guys suggest? I want good top end, but I don't want to sacrifice throttle response or low end? I am adding these mods because I want to increase the power of this 350x engine, I don't want to do all this work to it only to limit it by the new carb. Please let me know what you guy's think.

Thanks Truck, and Dill.

Brian

 

Hi there, sounds like fun.

In reading over your mods, I did not notice any reference to porting the head. Without this PowerRoll is probably correct about the carb. no point in increasing airflow cap. at one point without matching up the rest of the airstream.
I own two 350X/250X conversions, one engine is a 365 kit done by TC with a 44/38mm Lectron, engine ported to 33 mm, 12:1 piston. 924 cam and TC's latest cdi, Supertrapp 1 3/4" x 4" TC modified exhaust (no internal baffles, and billet open cap pipe on the silencer). The other one is a 425 kitted machine with a modified JE piston and head work to bring it to about 13:1,(was 14.3:1 until we changed it just recently) 36mm porting,a .315" cam modified by TC, Ti springs retainers etc. shortened valve stems and the same 38/44 TC/Lectron carb, a custom extra long header kit which goes out and around the frame supports hooked up to TC's standard 1 3/4" x 4" SuperTrapp. Lectron says they only build this carb for TC as it has some extra machining done to it for him - mostly on the outside bores I beleive to fit the stock air intakes and manifolds(which should be modified to realize the gains from the carb) but who knows for sure? better to buy it from TC racing to be sure.

According to Lectron this 44/38mm flows more like a straight 44 than a 38, due to a very high venturi efficiency caused by the intake and outlet angles. In a recent test the Lectron showed the highest overall hp gain. It was lower at low rpm but significantly higher at high rpm. Several things bother me about the test having mounted Lectrons. there was no discussion about what if any modifications were done to the inlet manifold. They are harder to mount because they are about an inch shorter, and have a long throw which requires mods to your throttle asssembly. This shorter length and large barrel also slow down velocity which would account for the diminished low end power in this test if mounted with a stock inlet manifold. I make my own manifolds from billet aluminum and mount an internal rubber shock isolator. When doing this I have increased the runner length to regain low end velocity, as well as being sure that all internal surfaces are free flowing (no lips). This mod also helps reach the standard airbox with the stock inlet tube, as it is too short using the Lectron and stock manifold.

My experience on 350X's is limited to these two carbs and the 38mm Keihin which I mention below. When I changed the Keihin for the Lectron, I saw an immediate gain in throttle response, and a more consistent performance throughout the power range (using the existing exhaust which was not SuperTrapp yet). I also put a larger modified stock intake (rubber) manifold on the engine to accomodate the larger diamenter Lectron. But the outlet was only 1 mm larger than the one which came with the Keihin. Neither manifold was optimized for either carb. In the Northeast where I live most of the modified 350X motors seem to be done by TC Racing, who is in Warren Pennsylvania. He has built specials for such notables as Travis Spader, and Doug Gust (not just 350X motors) who have campaigned these rides successfully in GNC.

When doing the Lectron conversions he matches up the airflow with a 4" x 1 3/4" SuperTrapp, which I beive has a "PowerRoll" headpipe design (looks like it to me). He also does the porting to match the new airflow.

Both bikes I own had their conversions done before I bought them, and so my work on them has been to check and see what was really done vs what was claimed to have been done, and then to update or improve upon these conversions.

PS I have the 38mm Keihin race carb and cable for sale ($100.00) which I replaced with my Lectron. It was on the 425cc. By the way the 365cc outruns most 265r's and some of the 330r's at the short 1/7 mile flat track where we race it.
The only quads faster are Sue Parkers new 330r, a heavily modified 725 cc raptor (which beat Sue Parkers 330r), a 490cc 400 ex conversion, and one other 330 r. We race this bike in open sportsman class as well as open 4 stroke. I have not tested the 365 with my new manifold, but have run the 425 a bit. The 425 is stronger than the 365, and appears to reach full rev's in about 60% of the time it did with the modified stock rubber manifold and everything else the same, but we have not done any accurate measuring on this conversion yet. We are going to have it dyno'd. with both the stock manifold and the aluminum one in a couple of weeks.