I have been reading the posts on removing the hac valve and jetting for altitude. I tried to adjust the hac valve as suggested on one of the posts. Measuring from the end of the tube at the end of the hac to the actuating pin. 3 to 7 mm. Mine was 9mm. Set it to 4.5 and the machine still didn't run right. Burned up 3/4 tank going just 29 miles. My question is, there are 3 ports on each carb, 2 that are 3/16 and 1 on the back of the carb that is 1/4 inch. Is the 1/4 inch line that goes to the top center port on the hac the vent line? If so does that port still need to be vented after the other ports are plugged? I orded 270 and 280 mains and 50 pilot jets today. Will set the pin on the second notch and turn the air screw to 3/4. Any info would help. Thanks
Hac valve removal on a 1997 summit 670
- Thread starter david670
- Start date
tripster
Active VIP Member
Those HAC valves always screwed up from new. Most of the guys I rode with chucked them and jetted for altitude. We also used to run these
If I remember right we were running 25 pilots with the ufo's and this eliminated the flooding issue the summits had when they were shut off facing downhill.
If I remember right we were running 25 pilots with the ufo's and this eliminated the flooding issue the summits had when they were shut off facing downhill.
2dawgsfawkin
Active member
do as tripster suggested while wearing a hat made of tin foil and you'll be fine
TROLLCAT
Active VIP Member
I would be starting with a larger main jet 320 - 340 for 2500ft
plug the 1/4" port
float bowl needs to be vented to atmosphere (hope that one made sense)
plug the 1/4" port
float bowl needs to be vented to atmosphere (hope that one made sense)
rsaint
Active VIP Member
The ufos take and throw them far away off a cliff been there and done it and never had a problem with the hac on the 670 take it to a dealer and get it calibated.
TROLLCAT
Active VIP Member
better to slowly jet down that it is to burn down
- Thread starter
- #7
TROLLCAT
Active VIP Member
plug the line that has the arrow pointing at it (found this pic on interweb)
Trollcat has the right specs and tube to block off, with the HAC gone you need to use the MXZ 670 chart for jetting, they start about 330's. The Summits were typically running around 410 mains, depending on the year, we used to run 380's comfortably. The MXZ's ran much smaller mains. Going to smaller pilots helped but the flooding pointing downhill is a float level issue, you need to raise the float level a few mm's if I remember correct.
- Thread starter
- #10
What needs to be done with the other ( 4 ) 3/16 lines on the carbs. Arn't they the ones that need to be plugged? Don't they change the vacuum in the carbuertors that causes a leaner mixture? I guess I'm confused. If anybody has a link to doing this it sure would help me out. Thanks again
TROLLCAT
Active VIP Member
leave the other 4 lines alone open to atmosphere
toss the HAC in the garbage
and there will be another line going to crankcase/stator leave it open, it is just a vent for the HAC
- Thread starter
- #12
First I want to thank Trollcat for the picture and info that he provided. Here is what I did to make the machine run at 10,000 ft. The ( 4 ) small 3/16 fittings on the carbuertors that attached to the sides of the T fitting coming off of the HAC valve are vent lines. All you need to do is buy a 3/16 T fitting from your hardware store and hook the ( 2 ) lines together with a 3/16 tubing to vent under the cowl. The 1/4 fittings on the back side of the carbuertors closest to the air box need to be capped. Now change out the piolet jets from #75 to #50. I changed the PTO side ( clutch side ) from the 370 main jet to 280. Changed out the MAG side ( flywheel side ) from 360 main to 270. I then dropped the neddles to the leanest notch which would be the top notch. The only other thing would be the tube coming off of the crankcase just in front of the flywheel. ( this was hooked to the HAC valve below the T fitting. This port is what the HAC valve senced the air temperture and altitude and made adjustements to the carbuetors. Just leave the line on the fitting and leave it open under the hood. This port doesn't go the crankcase, just open at the flywheel opening. Now I hope I can go more than 29 miles on 3/4 of a tank of fuel. Hope this helps anybody that is having problems with their HAC valve. I hesitated pulling the HAC valve off but glad that I did. Cost me $35 for jets and piolets.
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