May 18, 200620 yr Anyone know what jetts should be fitted in a Dellorto VHST 26 fitted to an 04 Rev3 200? The carb is one of the Beta tuning parts and I would think it comes jetted for the 250 or 270. The jets fitted are as follows: A S35 B 270K C 60 D 270 The one that holds the bowl on is a 170 and the needle is a D49.
May 21, 200620 yr Hello If I read you correctly: Idle jet S35 Needle jet 270K Needle D49 Main Jet 170 (seems small to me) Choke Jet 60 Float Valve 270 Firstly with a sharp knife cut the two pegs away on the inlet rubber. This is to assist carb removal and reassembly. Some oil on the carb inlet and outlet will help when putting it back. Taking the carb off, rejet and mount it back again can be done in 10 minutes. I would try the carb as it is. The first check the idle system. The idle should change when adjusting the idle mixture screw. 1-2.5 turns out is good. Then try to establish the correct main jet size by full throttle runs in 3th-4th gear. Four stroking tell you that the main jet is to large while hesitation tell you that you need a larger main jet. I guess the needle/needle jet combination is just about right and the only adjustments needed is the needle position. The engine must be in working temperature (check the fan) before performing any fuel set up tests. By the way, the VHST is sensitive to dirt. Use a fuel filter and keep the petrol clean. Hope this helps. Regards carl
May 21, 200620 yr Author Thanks Carl I have fitted the carb with the standard settings and by the plug colour it is very lean. It will rev out clean and idle well but on a steady throttle at low speeds it won't run smooth (the bike surges and slows). At idle the air screw has no effect at all. At the moment I have no idea as to what jets to change and what size to try.
May 21, 200620 yr The idle mixture screw has no effect telling us that the idling system is out of range . You say it surges. I guess you are correct when you say it runs lean. Try and open the choke at low throttle openings and see what happens. Try and run at slow speed. I have had new out of box vhst that need cleaning You may try and carefully blow all passages and jets with compressed air. Just a thought. The vhst is standard fitting to Beta 125
May 21, 200620 yr Author Thanks again, I see from a previous post that you have a 120 main jet fitted in a 270 and you think that the 170 in my carb seems small, is the larger number a larger jet?
May 22, 200620 yr Author Would changing the main jet to a smaller one make it run leaner than it already is? though I can't see that it needs a larger one! I think I should check that everything is clean first as I guess a blockage could cause it to run lean.
May 22, 200620 yr In theory the main jet has no effect at all at small throttle openings. The depression simply isn
May 23, 200620 yr Author I cleaned the carb fully and lifted the needle as far as it would go, now the mix is not as lean and the idle mix screw now has an effect though very slight. The power delivery on an even throttle is still pulsing though. I did the choke test but the engine just stalls.
May 23, 200620 yr Ok, Choke test=engine stalls. To me this tells rich mixture and no blockage in the idling system. If there is a blockage the engine usually runs better when the choke is opened. Chocke closed=running lean but idle mixture screw has an effect when needle is in 5th position. I would try one or two sizes larger pilot jet. I think you can get jets from here http://www.dellorto.co.uk Good luck. It
May 24, 200620 yr Author Thanks again Carl. Lifting the needle has improved things but I think it will still take a bit of fine tuning to get it perfect, should be worth the effort though. I'm still confused about the large main jet but the bike revs out clean so it can't be to bad.
June 1, 200620 yr Here is the Beta Original Factory 250/270 Tuning Part data: Dellorto VHST26BD R9359 Main Jet 111 Needle Jet 272H Needle D48 Idle Jet S38 Throttle Cut Away 55 Choke Jet 60 Spider 2.5mm The Air Jets also appears to be of different size from std carb R9354 Carl
June 2, 200620 yr Author Hi Carl, The carb that I have is one of the Beta tuning parts but some of the jets are not the same as you listed. The main jet is a 110 and not a 170 as I said befor (I think I need my eyes tested)I have changed it for a 118 and after setting the mix screw it seems to be a lot smoother now, I may still try a smaller idle jet as it is still a little rich at idle. thanks again for your help.
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