Carb size...

spincycle

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Anyone with any thoughts on if a 28mm alky tillotson might be too much carb for an animal motor with a stock piston/cylinder cut .015 over? Head has been ported with 32/28 valves with dual springs, roller 1.25 lifters and a 308 cam and stock stroke crank....kind of a low budget limited modified piece if you will...thx!
 
Anyone with any thoughts on if a 28mm alky tillotson might be too much carb for an animal motor with a stock piston/cylinder cut .015 over? Head has been ported with 32/28 valves with dual springs, roller 1.25 lifters and a 308 cam and stock stroke crank....kind of a low budget limited modified piece if you will...thx!
I think its perfect because your using a 32mm intake
 
I think its perfect because your using a 32mm intake
Agree, That's always been a rule of thumb I learned over the years...trying to dissect a big issue I'm having...motor is pushing a large portion of the oil (12oz) into the overflow tank, along with a fairly good amount of fuel...to the point of galling the rod bearing to the crank...thought maybe too much fuel in the cylinder washing cylinder wall to the point excess fuel is passing worn down ring and accumulating in crankcase then being pushed out vent lines into overflow leaving motor oil starved...sound plausible?
 
No . 12 oz of oil in the over flow tank is gotta be something else besides the carb size .
with additional fuel .
what diagnosis or tests have you done ?
Sorry, miss-communicated, starting with 12oz of oil in the engine, large portion of that amount along with a good amount of fuel being pushed into overflow tank after about 10 laps on the track...😵‍💫
 
28mm Tilly, that would be the hl 380 I guess with its 28 mm throttle bore. It is a lot of carb for a stock bore , but you can get by with it with a big cam. The problem your facing is if it's a factory alky drill pattern it's way too rich for an ohv. The carb was designed for a flathead open. The idle circuit has two feeder holes with one at .040 plus one at .028. Plug the .040, run the pop off about 10 that should stop it from washing the motor down with alky and build some engine heat.
 
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28mm Tilly, that would be the hl 380 I guess with its 28 mm throttle bore. It is a lot of carb for a stock bore , but you can get by with it with a big cam. The problem your facing is if it's a factory alky drill pattern it's way too rich for an ohv. The carb was designed for a flathead open. The idle circuit has two feeder holes with one at .040 plus one at .028. Plug the .040, run the pop off about 10 that should stop it from washing the motor down with alky and build some engine heat.
Plug with lead or epoxy ?
 
28mm Tilly, that would be the hl 380 I guess with its 28 mm throttle bore. It is a lot of carb for a stock bore , but you can get by with it with a big cam. The problem your facing is if it's a factory alky drill pattern it's way too rich for an ohv. The carb was designed for a flathead open. The idle circuit has two feeder holes with one at .040 plus one at .028. Plug the .040, run the pop off about 10 that should stop it from washing the motor down with alky and build some engine heat.
It was drilled and prepared for the ported 32/28 valve head by competition carbs...I've also got a 304wxa set up for alky that I ran on a stock size valve unported head motor...might need to try that carb instead?
 
I had the 28mm alky carb on a stroker crank/big bore/big piston bottom ended motor, it shot the rod last nite of summer season last year, when I got another bottom end together, is when I stayed with stock stroke/stock size piston, I ran it 2 times indoors over the winter without any issues whatsoever, first day of outdoor season, it pushed the oil out, put new ring, cylinder rehoned and new rod bearing in, ran 10 laps yesterday and again puked the oil out and locked up tight...🤨 I kinda felt the big piston set up felt kinda lazy coming off the corners, though had monstrous top end, thought to try smaller piston/bore set up for better faster power coming off corners...🥴
 
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After talking to the builder, I think we got to the bottom of the problem, our local kart shop sells their own labeled "heavy weight" oil...since mid season last summer, they have been out of it for reasons unknown, I had the motor built with the 28mm carb set up and big bore/piston at about that same time, I got some valvoline 20w-50 racing oil and used that without any issue for a couple indoor races over the winter...local kart shop finally got restocked with their own labeled "heavy weight' oil, the outdoor season started 2 weeks ago, I had used up the 20w-50, so I bought a gallon of the local kart shop (heavy weight oil, trying to give them the business), well, the combination of what is most likely too much carb for the motor and the lighter weight "house oil" just diluted the oil in the crankcase after washing down the cylinder wall, hence causing the oil starvation issue and subsequent motor failure....🥺 I do have a smaller tilly 304wxa alky carb to put on it after the bottom end is rebuilt, hopefully that should resolve the problem...🙏
 
Flattop , I've been using Marine tex for years with good results, an epoxy mix that can resist alky. Spin cycle, that's a bored 360 A , so it's got his drill pattern, but it's dumping way too much alky for some reason. The 304wxa should work better on that combo and will be lean enough for you to make some engine heat and run hard on top end.
 
I'm working on a 28mm Mik set-up on a stroker (big bore) animal currently. It's what I prefer with big valves and ratio rockers.

Spin, if you're getting too much fuel in the oil, it's almost gotta be drilled too rich on the bottom end (like a flathead pattern.)
I use the 304wx/a on limited with stock valves. I don't think it's enough carb for big CI opens, BUT, it will likely cure the over-fueling problem.
Tillys don't like to be idled, I don't care who drilled them. It's just a design thing. I suspect that the washing down of the cylinder is caused by too much idling and low part throttle. Avoid that as best as you can. As for oil -- stick with what you know works best for your application. Personally, I like Briggs 4T. Good ol' FHS 62R is a close second.

Jon, Thanks for sharing your insight. Much appreciated. I've never had much luck in epoxy and redrilling, but I've also not tried that particular product. As much as I hate to, I may have to go back through some old flathead carbs and try it now. :)

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🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
34 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
I'm working on a 28mm Mik set-up on a stroker (big bore) animal currently. It's what I prefer with big valves and ratio rockers.

Spin, if you're getting too much fuel in the oil, it's almost gotta be drilled too rich on the bottom end (like a flathead pattern.)
I use the 304wx/a on limited with stock valves. I don't think it's enough carb for big CI opens, BUT, it will likely cure the over-fueling problem.
Tillys don't like to be idled, I don't care who drilled them. It's just a design thing. I suspect that the washing down of the cylinder is caused by too much idling and low part throttle. Avoid that as best as you can. As for oil -- stick with what you know works best for your application. Personally, I like Briggs 4T. Good ol' FHS 62R is a close second.

Jon, Thanks for sharing your insight. Much appreciated. I've never had much luck in epoxy and redrilling, but I've also not tried that particular product. As much as I hate to, I may have to go back through some old flathead carbs and try it now. :)

-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
34 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
I had a big bore stroker animal, that's what I bought the 28mm alky carb for, when I ran it with that combo, it ran like a scaled ape, with minimal fuel in the oil, even after a feature with numerous yellow flag laps, entirely my fault, but that big bore/stroker set up shot the rod out the case on the last race of the summer season last summer, I had it rebuilt before indoor racing started, with stock stroke/stock bore bottom end (lacka fundzas disease), I was using 20w50 oil, and used it for the couple indoor shows with the big carb/small bottom end combo, ran great as the oil was heavy enough to handle the fuel buildup...without thinking much about it, I switched to a lighter weight synthetic oil, which was not thick enough to handle the fuel buildup from the 28mm carb...so there is nothing wrong with the drill/set up by competition carbs, rather a mistake entirely on my behalf by putting it on a motor combination it does not belong on...as Ole DW has said, it's a matter of "sperence"...
 
I had a big bore stroker animal, that's what I bought the 28mm alky carb for, when I ran it with that combo, it ran like a scaled ape, with minimal fuel in the oil, even after a feature with numerous yellow flag laps, entirely my fault, but that big bore/stroker set up shot the rod out the case on the last race of the summer season last summer, I had it rebuilt before indoor racing started, with stock stroke/stock bore bottom end (lacka fundzas disease), I was using 20w50 oil, and used it for the couple indoor shows with the big carb/small bottom end combo, ran great as the oil was heavy enough to handle the fuel buildup...without thinking much about it, I switched to a lighter weight synthetic oil, which was not thick enough to handle the fuel buildup from the 28mm carb...so there is nothing wrong with the drill/set up by competition carbs, rather a mistake entirely on my behalf by putting it on a motor combination it does not belong on...as Ole DW has said, it's a matter of "sperence"...
Maybe. If you changed base stocks when you changed your oils, that's more likely the problem with the catastrophic failure. Compressor oils don't play well with others. (before or after)
Tillotsons are notorious for putting fuel in the oil (especially if they are idled much.) How your oil handles that fuel contamination is a side effect, not the cause, for putting fuel in the oil. Fix the cause and even the cheapest oil will suffice. Maybe that means a leaner drill pattern, maybe it means a stroker crank / big bore shortblock in the future. For sure, all the players in the symphony must work together.
 
Spin , I just read back a little. You said that carb worked with no issues for two races over the winter on your little motor, then it sat till summer and now it's dumping fuel. Are you checking popoff to see if the needle and seat are sealed up? You can lean on those needle some for that small motor also. Comp knows his patterns.
 
Spin , I just read back a little. You said that carb worked with no issues for two races over the winter on your little motor, then it sat till summer and now it's dumping fuel. Are you checking popoff to see if the needle and seat are sealed up? You can lean on those needle some for that small motor also. Comp knows his patterns.
I'm not a motor wizard by any means, with that being said, when you say "sealed up", I don't know what that means...I've taken the carb totally apart and meticulously cleaned it, especially the needle and seat (can't tell you it was, but a person on here told me to put a small dab of toothpaste on the end of a qtip and insert and twist inside the seat), I've always done it that way with several different tillys over the years without ever having any issues...as far as pop off, I don't have a pop off gauge, I set the fulcrum slightly above level with the carb body and go with it, again haven't had any carb issues until this year, motor bottom end due back from engine shop next week, gonna reassemble it with my 304wxa on it and give that a run, I pretty confident the 28mm pumper was just too much carb for the stock head configuration I had on the motor to start the season...and yes, Dustin at comp carbs does a great job imo...spin
 
Finally had an opportunity to run the kart yesterday with the 304wxa carb on it...ran like a champion all day, very little fuel and/or fuel in the overflow, maybe down just a bit on hp, but would much rather have that than maybe 3 faster laps total then rod bearing seize...😁
 
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