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Metering Spring Mod for More Fuel Supply to Carb for all motors.

Discussion in HPI Baja Engine and Exhaust forum, started by Timmahh.

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  #1  
Old 05-04-2011
Timmahh Timmahh is offline
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Metering Spring Mod for More Fuel Supply to Carb for all motors.

Ok this comes up probably once every few weeks, so i dug thru and gathered the information neccessary to do the Metering Spring mod on your carbs.

for those that dont know, you can adjust the pop off pressure of the metering valve, which dictates amount of fuel flow into your carb at any point in the rpm range. by lessening the pop off pressure, you allow for less fuel pressure to be needed to enter the carb, thus makeing it easier for fuel to flow into, thus thru the carb, maximizing fuel available for the motor thru the entire rpm range.

This can be a very important mod on a Reed case motor, but due to all carbs being slightly different, it may or may not be an effect you have, or will ever have. but its good information to know, if your maybe having some quirks that you cant track down initiallly, and your swayed to think its fuel supply. a good indication your pop off pressure is too high is if your primer bulb is constantly being emptied out after a long run.

your primer bulb should basically be 1/2 full or more pretty much all the time. if you run, and see your primer bulb is empty or near empty, you will likely see great benefits to lowering your popoff pressure, thus increasing fuel flow, thus fuel supply to the carb and motor.

here are some of the posts quoted by the original poster, on their mods and subsequential results. at the end, you ll find a link to the relavent thread where i dug this information out of.

enjoy.

i took a bit of time and dug up the relavent thread and subsequential posts. these will help you imensly. Im actually going to make a new post on just this topic in the engines/exhaust section.

Quote:
Originally Posted by SSNOS View Post
I just started another thread with issues with my 813 and TS metering spring. The metering spring is under the primer bulb housing. If you take off the housing, you'll see the main needle and metering arm and the spring goes under the arm. I've had some tuning issues with this setup so my reccomendations would be for you guys to wait and see what TS says about my problem first before you try this combo. I think the spring is only meant for teh stock carbs.
Quote:
Originally Posted by stubby686 View Post
Update: The pump/gague set up I'm trying to use is less than fair to say the least so I'm just doing it the old fashion way ..... trial & error .

I'm taking single coils off the spring then running it to see if there is a difference. The first 5-6 coils didn't do a thing at all. I went for broke today and took 5 more coils off all at once. What a difference that made. It's not 100% ripping out of the hole on pavement but about 3-4 feet out it's all that & then some. On dirt with less traction about 1 foot out if that and all hell is unleashed !! The way I see it now it's perfect (for me). Who woulda thought snipping a few coils off a tiny spring could make such a huge difference. I was just about to dump 300 into a top end. According to Trevor the stock springs in the WT carbs need aprox 25psi to open the metering needle and the "sweet spot" is 12-14psi.

Thanks everyone !!! This thread saved me some coin , put a huge grin on my face seeing this thing rip & hopefully helped out someone else be it now or in the future !!


Quote:
Originally Posted by stubby686 View Post
Thats the one. #48 (NOT #48A). It can be done with the carb still on the motor. Just take off your roll cage & air filter.

Carb how it will be on motor , take cap off tank to release any pressure first


Take 4 screws out & remove bulb, white part of carb & diaphram (black gasket) Fuel line can stay on



Take the phillips screw out and you'll have the metering lever & spring in hand. It's a really crappy pic of the spring but the two ends where the coils are close together is what your after. I took about 5 coils off each end. That was aprox half of the total (close together) coils on each end. This is a 668 carb & looks to have a different spring than the 813 I've been messing with. My 813 spring had more coils wound close together on both ends but was shorter in total length so in theory would make it stiffer having more coils in a shorter spring. Anyhow all springs will be different as will personal set-up's so it's whatever works for your app and not a "coil count" as what to take off. I found a utility knife works best to cut the coils off. Lay the spring on something metal and put the blade in the spring where you want to cut it and rock the blade back & fourth while pushing down. The nail clipper way spreads the coils apart and bends them and was a PITA IMO. Good luck !!





Quote:
Originally Posted by KUN114 View Post
This is what I came up with. Not sure how accurate it is, but seems to work. I took a Ball needle, slid about a 1" piece of antenna tube over it. Then the fuel tubing over that and wrapped it all with some vinyl tape. Hooked it to my low preasure motorcycle suspension pump.

Stock spring popped at 30psi
Cut off 5 coils from each side brought it down to 26psi
Cut all close coils from each side= 20psi
Cut two more coils from each side and it's about 14psi
Installed the spring in the carb on my 5T and fired her up. Notice a major difference just running on my short driveway. To bad we just got 30" of snow yesterday, so it will be a while before I can give it a proper test run.
Another question. Will this spring mod benefit performance on any engine or just the reed port engines?
and the original thread link.
http://www.hpibajaforum.com/forum/sh...t=metering+mod


maybe this can be stickied up. would be a great sticky imo for anyone with a TS motor, or other Reed induction motor. as well as pretty much any motor that just doesnt seem to be all it should be.
Timmahh
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Old 05-04-2011
Demonik Demonik is offline
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I use the gold spring out of my 167 carb in my 668, but I never built the tester.....Is this the gold spring that TS uses? If not has anyone tested the popoff on this spring?

Last edited by Demonik; 05-04-2011 at 06:26 PM.
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Old 05-04-2011
Timmahh Timmahh is offline
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i think it could be, but i cant say either way with any certainty Demonik.
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Old 05-04-2011
Demonik Demonik is offline
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Ok thanks...here are some pics

Left spring is stock, middle is gold out of 167, right one is out of another walbro



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Old 05-04-2011
ReubenB5T ReubenB5T is offline
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i'll be giving this a try on my new reed case motor... got a few extra carbs laying around to play with...
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Old 05-04-2011
towner777 towner777 is offline
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I chopped a few coils off mine, just a regular 29cc.. And it really helped all around, mostly low end though.
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Old 05-04-2011
mike the snake mike the snake is offline
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Does this mod change the needle settings?

I'm always needing more low end power.
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Old 05-04-2011
Timmahh Timmahh is offline
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yes, once you make this mod to your metering spring, you WILL want to retune. your adjusting the fuel flow into the engine, so you ll want to retune for the best performance with the new amount of fuel.
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Old 05-05-2011
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Nice work Timmahh
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Old 05-05-2011
mike the snake mike the snake is offline
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Is this mod primarily for reed case engines?

I have modded stock engines, but if there's more low end power to be had, I'd be willing to play around with this carb mod. Right now I run the stock 668 carbs with no complaints, but more low end power I can always use.
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Old 05-05-2011
01bluerado 01bluerado is offline
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hhmmm this may be worth a few minutes of work if i can gain a little low end
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Old 05-05-2011
Timmahh Timmahh is offline
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this mod can help any motor that may be not getting enough fuel flow to and thru the carb.
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Old 05-05-2011
DogPile Racing DogPile Racing is offline
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Nice post, I recently went through this on a TS engine a couple weeks ago. That little spring makes a huge difference in the way your carb delivers. Not a solve all solution but a step in the right direction.
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Old 05-07-2011
Timmahh Timmahh is offline
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ya pretty much. Its good to have a pop off tester like the one made above to check the pop off pressure once done. 15psi is about the sweet spoot. most stockers are around 25psi.
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Old 05-14-2011
cris cris is offline
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does that spring come in a rebuild kit. i tried this mod today and it bogged like hell on take off then came alive. i think i cut it too short lol.
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Old 05-14-2011
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that sux, guess im screwed now. dont wanna buy a 50$ carb
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Old 05-14-2011
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Quote:
Originally Posted by Timmahh View Post
maybe this can be stickied up. would be a great sticky imo for anyone with a TS motor, or other Reed induction motor. as well as pretty much any motor that just doesnt seem to be all it should be.
Timmahh
Nice work Tim and great mod!

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Old 05-14-2011
HdzrtBaja HdzrtBaja is offline
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Not sure if anyone has check but you can buy the walbro spring kit. (asortment of springs)

http://wem.walbro.com/walbro/partnum...anuItemNumber=

there are cheaper places to buy.
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Old 05-22-2011
baja_chief baja_chief is offline
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has anyone tried cuting off all the compressed spring and just leaving the extended coils?
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Old 05-22-2011
MCRIPPPer MCRIPPPer is offline
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Quote:
Originally Posted by baja_chief View Post
has anyone tried cuting off all the compressed spring and just leaving the extended coils?
this will get you in the ballpark. iv got a modded spring that is less then half the length of a stock one, and it pops at 15psi, so cutting the solid coiled ends should help alot.
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