Greetings! I haven't been on this site too long - about 4 hours I think. Most of that 4 hours has been spent looking for the info I need on swapping a different carb onto the 5hp B&S flathead we shoehorned into my Dad's Doodle Bug. I rebuilt the carb that is on it - one of those weird long ones that mount to the top of the tank. Cooked it in my ultrasonic cleaner for an hour and made all new gaskets for it. Seemed to go together just fine, but there was a metric ton of unnecessary carb linkage. There was the two sliders pictured (one for choke, one for throttle). I disconnected the linkage for the throttle but left the choke linkage since the engine requires choke to start even when hot. There was another remote throttle linkage setup near the base of the engine - removed all that. The bike just runs like crap. It will barely idle, sputters off "idle", has decent power through mid range, and then starts surging and sputtering at WOT. I really don't want to use this carb. I hate that I'm required to have the tank where it is. The doodle bug is a small frame, and we were limited on where we could mount the engine because of all the crap hanging off the back of it. I found several references to B&S #691922 intake adapter, but I don't think that will work for our application. This B&S (emphasis on the BS) carb has a weird bolt pattern - One bolt hole at 11 o'clock and the other at 5 o'clock. The 5 o'clock hole is spaced further from the intake bore than the 11 o'clock. I know I can probably make an intake that will fit just about anything with a silicone sleeve, but is there a commercially available adapter to put something like a predator carb on this B&S? I'm intimately familiar with the honda clones, and I have always had really good luck with them. Plus, I can get a brand new clone carb for ~$15. Sorry for the really bad pics - the breather box is super close to the backbone and I don't want to tear it back down right now just to get a pic of the carb bolted to the engine. Thanks for any help you can give!
Been searching around for info on a carb swap
- Thread starter RecoilFreak
- Start date
Just read the warning post on modifying engines without using a billet flywheel. Anybody know where to get one for this same engine? I definitely don't want Dad straddling a hand grenade with a hair trigger. I traded for this Doodle Bug for him because it reminded him of the mini bike he got into all kinds of trouble with in the early 60's. The last thing I want is for him to get hurt on it.
The Briggs carb is commonly called a "Pulsajet". It has, in different variations, been around for 50 or more years. It is pure simplicity. IF you have a lawnmower or other industrial use. It was not made for quick throttle response. There are kits available, for replacement, or you can buy the parts and assemble the unit for a little less. Either way, it will require the use of a remote fuel tank. Try OldMiniBikes of Go-Sports for the kits. Others have them too. Or, you can buy a Briggs intake and a Mikuni (or clone), to build your own. The Briggs intake manifold is part number 691922. Make sure it fits your port, there are some differences.
Thank you! Yes, the main reason for switching to another carb is to relocate the tank. I'd like to get one of those cool little spun aluminum jobs like Moon makes and mount it sideways either sitting on the rear grab handle or just under the rear of the seat hanging from the frame rails. You ain't kidding on the response - the throttle is more of a "suggestion". On the bright side, it has way more power than the lil 96cc 2.8hp squirrel cage that came on it. I have a feeling we will be burning through the brand new clutch before too long. I haven't done anything to this bike other than swap the briggs onto it and convert to #41 chain, and it's as fast or a little faster than our 40mph Warrior. Talk about pucker factor... riding that tiny squirrely rocket with 6" wheels and knobbies at 40mph reminds me I am not a kid anymore, and won't bounce like one.
Does anyone know if a Mikuni VM26 will bolt up to B&S 691922? I can’t find measurements of the carb flange holes anywhere. A VM26 is 48mm center to center.
P.S. - If anyone has one of those cylinder fuel tanks collecting dust, I'd love to take it off your hands. Apparently the new ones are lined with gold foil.
Does anyone know if a Mikuni VM26 will bolt up to B&S 691922? I can’t find measurements of the carb flange holes anywhere. A VM26 is 48mm center to center.
P.S. - If anyone has one of those cylinder fuel tanks collecting dust, I'd love to take it off your hands. Apparently the new ones are lined with gold foil.
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This is what I bought:
https://www.amazon.com/gp/product/B07G915FNB/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
It's a little misleading, in that it quotes it's a VM22 "style" carb, but is 26mm. It also says it's intended for 110cc-140cc engines (chinese pit bikes). I also ordered main jets for it. No idea what comes in it, but Mikuni lists their VM22 as coming with a 100 main jet. The jets I bought in addition to this carb range from #88-#125. Hopefully I can make it run right. It appears that this is pretty standard as far as chinese knock offs go. I could not find a 21 or 22mm carb without going with Mikuni. I am not willing to put that much cash into this lil thing right now.
https://www.amazon.com/gp/product/B07G915FNB/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
It's a little misleading, in that it quotes it's a VM22 "style" carb, but is 26mm. It also says it's intended for 110cc-140cc engines (chinese pit bikes). I also ordered main jets for it. No idea what comes in it, but Mikuni lists their VM22 as coming with a 100 main jet. The jets I bought in addition to this carb range from #88-#125. Hopefully I can make it run right. It appears that this is pretty standard as far as chinese knock offs go. I could not find a 21 or 22mm carb without going with Mikuni. I am not willing to put that much cash into this lil thing right now.
My mistake. I should have said it's a PZ22. I failed to indicate the designation, just the size. http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=283200901814
as far as a 22mm I bought a genuine mikuni vm22 and it took some tuning new jets and I had to swap the needle but runs perfect now. I've heard the mikuni taper boar carbs that taper to 26mm are commonly mistaken for vm22s, they are allot different but Ive herd they still run great. and usually don't need a needle swap. as far as the billet flywheel arc racing has them and they are the only ones I know who make them. I run the cheaper version without the adjustable hub and it works great. and get one of there billet rods also. the stock rod is just as dangerous as the flywheel. I got my current intake from a member hear named dave wolf but I don't know if he still makes them.
my current setup : billet rod, billet flywheel, dyno cams 107ss cam with the recommended stronger springs. ported intake and exhaust shaved head mikuni vm22 and a header from Roberts torque tubes. this is a very fast setup I can outrun a stock over head valve and keep up with and even outrun some of the un governed ones but a fully built over head valve still leaves me in the dust.
my current setup : billet rod, billet flywheel, dyno cams 107ss cam with the recommended stronger springs. ported intake and exhaust shaved head mikuni vm22 and a header from Roberts torque tubes. this is a very fast setup I can outrun a stock over head valve and keep up with and even outrun some of the un governed ones but a fully built over head valve still leaves me in the dust.