Search the Community

Crf100 with a BBR 120 kit, web cam 68/69 cam, Keihin 24mm carb that I’ve been running it successfully for a few years now. It has been amazing. I made some recent upgrades. The main two that might lend some help answering the questions are lightened fly wheel and I port and polished the head. I have built many motors and this one was flawlessly put back together twice since the noise. There is zero valve tap, no bent valves, cam lobes are perfect, springs are perfect, timing is spot on, there’s a ton of compression, no dents in the top of piston from possible valve, and valves are lashed perfectly. Any help would be greatly appreciated.

So I’ve got a klx 125 that I’m fixing for someone they told me to get it running so first thing I did check spark plug needs a new one but should be fine for testing purposes then cleaned the jets after this I got it to start but was back firing after deceleration so cleaned the carb again just to make sure jets were clear then it wouldn’t start unless bump started so I made sure fuel air screw’s were adjusted after I thought it had to be mechanical so I checked the valves the exhaust was off a little so I adjusted it and then it started right up again still backfiring so I shut it off and tried to start it again(didn’t start) unless bump started step 3 timing chain??????? I don’t know what to do next so what do you guys think?

Hi there! I wanna put some new valves in my old training bike - 2010 CRF250R. My main question is, what parts I should buy - what parts I should replace? FASTHEADS offers a rebuild, were they use the follwing parts: Beryllium Copper Intake Seats, Bronze Manganese exhaust guides, Chromium Nitride Coated Ti intake valves, Kibblewhite Black Diamond exhaust valves, OEM springs. They change the intake seats to actually match the titanium intake valves (stock seats are not perfect for the Ti intake valves) New exhaust guides, because they are mostly gone because of the rocker arm They leave the intake guides and exhaust seats (probably just re-cut them). --- Thats what I have on my list: New titanium intake valves - Del West or Xceldyne ? New intake seats - Beryllium Copper or MoldStar®90 (Beryllium-Free Copper) ? New exhaust valves - OEM Honda or Kibblewhite Black Diamond ? New exhaust guides - Bronze Manganese or MoldStar®90 (Beryllium-Free Copper) ? New valves springs - OEM Honda or...? When everything is true what they say about the MoldStar 90 stuff it's better than BeCu. Is this enough or should I replace everything seats and guides intake/exhaust? Any advantages if I go all titanium intake plus exhaust valves? Don't think so... Thanks in advance 😉

2006 ktm exc 250f The symptoms: - cutting out - sputtering - losing power - starting great sometimes - stalling in idle sometimes - battery eventually dying - clicking sounds sometimes I’m thinking either: valve adjustment / carbie rebuild / new starter motor / new fuel pump? Absolute noob here! The Detail I bought a 2006 ktm exc 250f and it ran for 2 hrs great on the road other than minor starter issue. Then at about 70km/hr it cut out. Had trouble stsrting but eventually got going and then it happened 3 more times on the way home. It looses power - so pulling on the throttle it just doesn’t respond. Took it to the mechanic they had no idea- said do a carby rebuilt but I didn’t trust them. They gave it a clean and I serviced plus got a new battery. Took it offroad after and it started, ran good for 10 min then lost power like before. After trying to start a while it eventually completely died. Making a slow turning over sound when pushing the electric starter and no luck with kick. My partner jumper started it (i.e.with cables), we let it idle a while (it needed lots of revs to keep going) and upped the “rev counter”. For 3 hours it ripped!! Went like a beauty, stalled in idle sometimes but otherwise I was in love. This weekend, it started fine but cut out after idling a little while. A lot of effort later got it started again but stalled it straight away because I was in sand for the first time oops! Now its dead and won’t even tick over. Help!!

I just started working on a trx450r I believe it is a 2005. It has the older carb as well. It sat for a while so I went in a rebuilt the carb and went to check the valves. The exhaust valves were alright but the intake had no clearance and had a 120 shim in it so there is no adjustment. So then I threw it together and went to take it around the block. Runs great when cold but as it gets hot it has a bog like reaction if I go past 1/4 throttle no matter what. But it runs great when cold. I’ve been told this is valve float and is actually common on these. Just want to make sure before I go out and spend 500 to get new valves and seats. Either way though I’ll have to get a head job done :(

It's time to open up a can of worms and talk about a hotly debated topic in the powersport community - four stroke cylinder head reconditioning best practices. I've perused the forums and had discussions with people about reconditioning four stroke cylinder heads and there appears to be a lot of mixed opinion and beliefs on what is right or wrong. I'm certainly not going to say my take on the subject is the only way, but I do want to share my opinion, explain the technical details, as well as touch on the machining process. The text below is out of my book, The Four Stroke Dirt Bike Engine Building Handbook, and details why cylinder heads should be reconditioned a certain way. Whenever new valves are installed in a cylinder head, it is best practice to recut the valve seats since the valves and seats are mated parts, otherwise the new valves are very susceptible to premature wear when run in the old seats. If a major overhaul is being performed, there is a good chance that enough seat wear will have occurred during the engine’s life that the valve seats will need to be recut before new valves are installed. This may be news to you, so I want to provide an explanation of why this is necessary. The term concentricity is used to describe the relationship between the axis of two circular objects. When two objects are perfectly concentric, their axis match up precisely with one another. In the case of the cylinder head, the valve guide axis and the valve seat axis must be as close to perfectly concentric as possible and parallel to one another. Usually, guide to seat concentricity is kept around 0.001” (0.025mm) or even less for racing applications. This is achieved by the factory by using a manufacturing process where the valve guides are reamed first. Then the freshly reamed valve guide bore is used to center the valve seat cutter. Once centered, the valve seat is cut. This process is then repeated for all the valves and results in very good concentricity between the valve guides and valve seats. As the engine is run, the valve guides, valve seats, and valve faces will wear. The valve guides will wear from front to back in an oval shape at the top and bottom of the guides. In a cross sectioned view the valve guide will take on an hourglass shape. The guide will become oval as a result of thrust forces stemming from the way the camshaft contacts the lifter bucket or rocker arm. These forces are transmitted to the valves and cause the valves to thrust against the sides of the guides, eventually causing the guides to become oval shaped. Once the guides start to become oval shaped, the valve faces will no longer be as concentric to the valve seats as they originally were. When this happens the valves will start to slide against the seats, causing the seats and valve faces to wear. The valve seats will eventually become out of round and the sealing between the valve face and seat will suffer. Installing new valves into oval shaped guides and out of round seats will ensure that the new valves wear out very quickly! To ensure the new valves being installed last as long as possible, the cylinder head’s seats and guides must be reconditioned once they are worn out. Complete cylinder head replacement is always an option, but I want to focus on freshening up the original head which is usually a more economical option, but comes with many more variables surrounding the quality of the job. There are numerous services offered in the marketplace for valve seat cutting, however, not all valve seat cutting methods are equal in terms of quality. There are hand operated seat cutters, dedicated seat cutting machines, and a few other options to choose from. Selecting the correct seat cutting process and entrusting the work to a competent engine builder is very important. The valve seat cutting process should mimic the OEM process as closely as possible. A concentric valve seat will never be able to be cut without first servicing the valve guides. If the valve guides are out of round then they will either be reamed to a slightly larger size if they are not too oval in shape or they will be replaced. Once any issues with the valve guides are addressed and they are perfectly round from top to bottom, it will be possible to cut the valve seat. Ensuring the valve guide is perfectly round is extremely important since the valve seat cutter is centered off of the valve guide bore. Cutting the valve seat concentrically to the guide requires a combination of skill and using modern machinery. The best valve seat cutting equipment in the world is worthless without a good experienced operator running it. There are two main factors which make cutting a seat concentric to the valve guide difficult. To start with, the valve seat cutter uses a pilot which locates in the valve guide. Since the valve stems are very small in diameter the pilots used to guide the seat cutters are also very small in diameter. A small diameter pilot shaft that centers the cutting tool can flex easily, which presents a real problem when cutting the seats. The next issue that arises when reconditioning seats is that often times the cutting tool will try to follow the path of the old valve seat which can make it hard to cut a concentric seat. Couple these factors together with slop within the machine, setup error, and operator error and you can see how quickly things can come out of alignment and you can end up with a poorly cut seat. In addition to seat concentricity, the depth the seat is cut to will influence valve spring pressure, shim sizes, and the compression ratio of the engine. All three of these variables will be reduced the deeper the seat is cut, which is not a good thing. The surface finish of the seat itself will influence how well the valve seals. A seat with chatter marks or other machining blemishes will not seal as effectively as a smooth seat. The valve seat width and the contact point between the seat and the valve face are also very important. Due to the complexities involved with cutting valve seats on modern four-stroke dirt bike engines, the job should not be left up to just anybody. There are numerous businesses which specialize in valve seat cutting which have both the right equipment and expertise to do the job correctly. I highly recommend spending some time researching and finding a reputable cylinder head machining company when it comes time to recondition your head. If the cylinder head must be shipped off in order to do business with a reputable company, the additional wait will be worthwhile. If you found this information helpful and would like more technical info on maintaining your four stroke engine, check out my book, The Four Stroke Dirt Bike Engine Building Handbook. Thanks for reading and happy wrenching! As always if you have comments or want to share your thoughts please leave a note below. -Paul Available at: - Amazon - Moto Fix Website