This weather hurts my engine's performance!

Minimichael

Minimichael

Well-Known Member
#1
#1
Both my three and five horsepower Briggs flatheads are running like crap and in fact the five horse just won't keep running even when it might occasionally turn over. It started last week when the humidity spiked around Chicago. High 60 percents, and hot. It's like the air no longer wants to flow or aspirate with the gas or I just don't know what. It may be the longer intake runner. I know. But I'm at a loss for how to tweak the carb – a VM22-TYPE – in order to counter-compensate here, around this uncooperative state of the atmosphere? Open vs restrict air.. Richen the slow jet.. Raise the needle.. I feel like I'm just guessing here. Anyone out there with a better grip on this? It's so hot here I can barely think straight...

PS, my 3hp has a vm22 on a short manifold and seems peppier once I turned the air screw clockwise about an eighth turn. A clue?
Screenshot_20260524-193251.png
 
Thepaetsguy

Thepaetsguy

Well-Known Member
#2
#2
I don’t believe it‘s heat.

I’ll give out the cheat codes

691922 3 hole briggs intake
Stihl ts350 vintage concrete saw carburetor
Genuine Tillotson rebuild kit

The ts350 has its issues you need a throttle bracket. And you need to use a pulse pump.

I have my pulse pump gravity fed off the tank. this carburetor setup works like you would not believe. kart sets for weeks starts second pull with choke.

No hassles strong idle runs 20+ miles up to the highway entrance AND BACK. Since I have built this Briggs for the red kart I have NEVER ONCE had ANY Issue with the ts350 cutoff saw carburetor.

As long as you rebuild it correctly this is the hot ticket.
IMG_7084.jpeg

IMG_3689.jpeg IMG_7148.jpeg IMG_7149.jpeg IMG_7581.jpeg
 
Minimichael

Minimichael

Well-Known Member
#3
#3
That's some good food for thought. Go to a different carb. Thanks. 3 hole briggs intake? I'm not familiar but will look. I suppose that may fit my three horse since you note your model no., too. Will look these up.
 
Last edited:
Havasu Dave

Havasu Dave

Moderator
#4
#4
I assume both engines used to run fine? Nothing in the weather has caused your problems. Yes, pressure density does affect performance, but not to the point of not starting or barely running.

Drop the bowl, remove the pilot jet and run a needle through it, or better yet jet or gas torch cleaning needles. The VM22 will clog that jet just by you thinking about it. Don't just blow air through it. You have to actually run something through it. This only affects idle, so i

As far as the other carb, you leaned idle out a bit.

Weather comment: It's been nearly 50% humidity here, with temperature over 100F. None of my bikes ever change, from minibikes to motorcycles, most of them on Mikunis. It did not used to be this humid here. My swamp cooler now barely helps.
 
sparkwizard

sparkwizard

#5
#5
I live near the east coast with near 90% humidity all summer. No changes needed to any carb on any engine. Dave's advice, above is great and I would follow his guidance, but I would read the plugs before tearing the carbs apart. That way, I KNOW it was lean. Good luck.
You posted a similar thread last summer. Did you find a solution, or just park the bikes?

EDIT* None of my engines are VM22 equipped.
 
Last edited:
Havasu Dave

Havasu Dave

Moderator
#6
#6
sparkwizard said:
I live near the east coast with near 90% humidity all summer. No changes needed to any carb on any engine. Dave's advice, above is great and I would follow his guidance, but I would read the plugs before tearing the carbs apart. That way, I KNOW it was lean. Good luck. You posted a similar thread last summer. Did you find a solution, or just park the bikes?
Click to expand...
To remove the pilot jet, it's four JIS screws, remove the bowl, remove pilot jet. Unless it's in a modified Hodaka, then you have to remove the entire carb. I think I had over ten VM22 equipped bikes at one point, and almost every single one of them would require that pilot jet to be reamed, because the pilot jets on these smaller slide carbs is microscopic, and everything clogs them. I made it a practice to run them dry, which helped, but there are a lot of legitimate experts out there who state that the only way a VM pilot jet doesn't clog is to use that fancy fuel sold in cans at hardware stores.

Anyone familiar with that carburetor can rebuild one in five minutes. Reading the plugs after repeatedly trying to start an engine will not reveal anything of value, other than if it is wet or it's dry. Remove the plug, squirt a tablespoon of gasoline in the hole, see if it wants to run. Agree with lean/rich reading of the plug for most issues. This problem should be easy to find, though internet troubleshooting leaves much to be desired.

Float settings/clogs can have a profound effect on these carbs as well. I'm not trying to sound smart, or super mechanic, but I do know these systems, and since my OCD is safety wired to the full on position, I tune these bitches to a gnats ass, which is pretty small. Yet larger than a VM pilot jet orifice.
 
Skipp

Skipp

#7
#7
Minimichael said:
Both my three and five horsepower Briggs flatheads are running like crap and in fact the five horse just won't keep running even when it might occasionally turn over. It started last week when the humidity spiked around Chicago. High 60 percents, and hot. It's like the air no longer wants to flow or aspirate with the gas or I just don't know what. It may be the longer intake runner. I know. But I'm at a loss for how to tweak the carb – a VM22-TYPE – in order to counter-compensate here, around this uncooperative state of the atmosphere? Open vs restrict air.. Richen the slow jet.. Raise the needle.. I feel like I'm just guessing here. Anyone out there with a better grip on this? It's so hot here I can barely think straight...

PS, my 3hp has a vm22 on a short manifold and seems peppier once I turned the air screw clockwise about an eighth turn. A clue?
View attachment 329765
Click to expand...
I just read about this yesterday….here I’m at 97 with 80 humidity and the dew point is 75….which translates into a walking shower as the feel like temp is 106….so my point is, is that the moister in the air really fucks with you fuel/air mixture…my eagle is fine until wot then is where the issue lies….ive adjusted these mt carbs up and down all week….my best suggestion is to leave them where they run best the majority of the time….unless you just like adjusting to weather conditions….just my opinion….ride slower
 
Havasu Dave

Havasu Dave

Moderator
#8
#8
Skipp said:
I just read about this yesterday….here I’m at 97 with 80 humidity and the dew point is 75….which translates into a walking shower as the feel like temp is 106….so my point is, is that the moister in the air really fucks with you fuel/air mixture…my eagle is fine until wot then is where the issue lies….ive adjusted these mt carbs up and down all week….my best suggestion is to leave them where they run best the majority of the time….unless you just like adjusting to weather conditions….just my opinion….ride slower
Click to expand...
Yup, But he's got actual problems if his engines are not starting. Of course this subject is a major reason ECU and EFI are so good. This is compensated for both in intake, and fine tuned via exhaust. (IAT, O2 Sensor) 97F @ 80%. A lot like some some tropical places I've lived.
 
Thepaetsguy

Thepaetsguy

Well-Known Member
#10
#10
I could verify the valve lash head gasket and bolt my Tillotson to your 5hp and i guarantee it would fire right up and run great all day long.

Even the china Mikunis will work absolutely flawless if the engine is sealed up correctly.

Briggs has a two and three bolt intake pattern. the 3 bolt pattern being the later. Intakes are not swappable between 2-3 bolt I don’t believe.

It really is sad you’re not close enough I can’t just pop over to your place and do the quick carb swap. You experience a correctly setup ts350 stihl carburetor those slide carbs would go in the trash I flat out promise.

IMG_7583.jpeg
 
Minimichael

Minimichael

Well-Known Member
#13
#13
Well it'll be a couple days before I can get back to it, but I'll start with cleaning the pilot. I put some fine tuning into that VM22 to get it to where it's at today. It usually runs strong and steady. I'm also looking at the Tillotson option, if just to compare how it performs with this extended manifold in my current setup. Maybe I'll learn something more there, too. Thanks for all the comments. Everything makes sense and seems a possibility. The condensation risk is plausible, for sure. And I still say this VM22 is crapping out whenever the atmosphere spikes into high humidity and heat. So maybe for sure corrosion, what with that high volume of wet air pumping through and causing the carb itself to feel sweaty kind of refrigerated at times (now that I think about it). Thanks again all. Happy Fourth coming up!
 
Last edited:
RiderZ

RiderZ

Well-Known Member
#14
#14
I agree with you Mike, since the high humidity and dew point jumped.
My bike's run like crap, I've been tuning with the air/fuel screw and needle height.
Funny, the Ghost not too affected but the 6.5's need tuning. They are inhaling a lot of water in the air.
 
sparkwizard

sparkwizard

#15
#15
I have quite a few Tillotson carbs. I got some from old chainsaws that are diaphragm type carbs, but without the pump. They are HC type carbs, and they are gravity fed, so no pulse hole needed. No real need to swap jets and needles and other tuning exercises. Just turn the HIGH screw, turn the LOW screw and adjust the idle. You can actually tune it out in the woods, if needed.
 
Minimichael

Minimichael

Well-Known Member
#17
#17
I
Harquebus said:
Eliminate one of the variables mentioned in post #11; cease and desist from using ethanol blended gasoline:
https://www.pure-gas.org/
Click to expand...
I get ethanol-free gas from the local airfield. But the moisture involved in the air certainly reveals itself during high humidity in the form of sweat collecting on the outside of the mikuni. Thinking now that maybe some makes it into the bowl and jets and corrodes and clogs.
 
Last edited:
Minimichael

Minimichael

Well-Known Member
#18
#18
Also just bumped into an old friend here in the Midwest and we got to talking about his Honda Monkey 125 and how it runs like crap in high humidity. And before we even got into any more facts he predicted the thick wet air just doesn't want to mix with gasoline. My own theory handed right back to me ;)
 
Minimichael

Minimichael

Well-Known Member
#19
#19
In fact, maybe a thinning additive like alcohol/ethanol could help the mix achieve an easier droplet/dissolution rate ... Just to look at it from a different angle.
 
Last edited:
sparkwizard

sparkwizard

#20
#20
Minimichael said:
Also just bumped into an old friend here in the Midwest and we got to talking about his Honda Monkey 125 and how it runs like crap in high humidity. And before we even got into any more facts he predicted the thick wet air just doesn't want to mix with gasoline. My own theory handed right back to me ;)
Click to expand...
Like the air is already saturated???? That is a thought I will ponder. Maybe even take it to the mad lab with my 12 year old scientist.
By Jove, You might be onto something, Sir!

Oil companies used to produce winter and summer gas blends. The winter gas was "thinner", more easily evaporated in the frigid air, and summer gas was thicker to reduce preignition and pinging (I think that was the reason). I wonder if humidity played into that formula.

In High scool in the seventies, shop teachers told students that car engines ran better on rainy days because they liked the cool, humid air.
 
Last edited:
You must log in or register to reply here.
Top