WT-990 mod on the cheap

[alfred e numan]

Its cool to see a few members porting there own jugs.- someone had mentioned bout engine bog after there mods. Yes, it could be a exhaust issue- who knows? Heres a cheap WT-990 mod. Its the pressure spring under the fuel bulb-gasket- AKA pop off valve.- This pressure spring has 2 functions- pressure release and reseat pressure.- I can explain further if you ask. The pop off pressure on the stock 990s i have tested is about 32 psi. this is quite high. The reseat pressure is bout 28 psi. IF-IF your 990s fuel bulb is 1/2 full to 3/4 full while ideling- after shut off. Heres the .50 cent mod. go to ddm site, enter this number on his new search engine-- 98-344. This spring will change the pop off pressure lower- the carb will enter fuel enrichment sooner- This springs pop off pressure is approx 24 psi. Its re-seat pressure is 17 psi. This is not gonna hurt your engine folks, it will just make feed more fuel sooner. I must stress this to you, do not pull springs off old weed eaters-chain saws- leaf blowers or start cutting or streching springs, it aint worth the risk- yea, spend a extra .50 cents on your next ddm order- give it a try!! agan- ddm has new search engine- just enter 98-344. Thought i would toss this out to you before i hit the hay tonight.- A.E.Numan.

 

[Guest]

You always have great info. I'm going to pick one up and give it a try.

 

[Guest]

As long as we are talk'n about the 990, I noticed that DDM sells a modified version that had bearings installed on the throttle shaft to eliminate dust entering at the throttle shaft. Out of stock currently. Looks good. http://shopping.netsuite.com/s.nl/c.885035/n.1/it.A/id.10610/.f

 

[creepingcharlie]

I am going to give this a try also. But doing this mod I am going to assume that the carb will need to be retuned . Will this also affect the fuel delivery in the high rpm range.

 

[BertR]

That is some good info and will have to give it a shot. The only problem I had was in the upper RPM I had a flat spot that took a few seconds to pick up and carry through

 

[BertR]

Hahaha look at the time of submit from us lol.

 

[creepingcharlie]

Damn right on the money. Lol.

 

[alfred e numan]

yes, you will have to re-tune the fuel screws. If you have never done this before, just remove the front part of the cars roll cage. best do thin where there is no carpet on the floor too.- If you have your old hy carb laying around, practice on this so you get the method down good. A big help is to magnatize the phillips screwdriver you will use to remove -reinstall the small screw - mount the screw on the philips -have it ready when you are holding this assembly with one hand- then place the screw in the thread hole. Its unknown if ddm has other springs besides the one i mentioned.- walbro makes several springs that are slightly stronger than the 98-344. example is-- 98-304. 30 psi pop off- 19 psi reset. Here is one reason its important to not try to mod-cut cut strech coils on springs--The re-seat pressure should be 10- i say-12-to 15 psi more or less. This will ensure that the fuel pump pressure does not override the needle since the fuel pump pressure is 5-7 psi. In other words- it will flood the engine.

 

[Chief409]

Thanks! I'll get one of these when I place my next order at DDM.