Union Bay 770 engine

If it has all the suporting mods or the air intake and the U.B.R cyclenders it should make around 160 hp. If you need any thing for service parts call kurt at fastrax racing they bought unionbay back in like 04 or 05. That 770 is based on the polaris 700

With the 68 mm stroke and big bore 85 mm jugs . So the stock 700 bottom end will be easy to find if ever there are problmes .

770

I built one of these several years ago and am still running it. Only problem I have had is the jetting. I have 2000 RMK 800 rack carbs on it but I can not get the low end right. It flat ripps from 1/4 throttle on but right off of engagement it is just flat. Hits like a motto cross bike when you get it out of this bad spot. Wondering if you have these carbs also and have looked what is inside of them? I am at 2000' and am running the non-ves 800 rack carbs with 02 800 XC jetting per Engine-Tech specs with power pacs in them. Larry Rugland twin pipes and can. I am going to pull the power pacs and see if this is the problem. I am running 560 jets and am still rich but my pyros say I am way lean. With the 9DFH10-57 needles in number 2, 45 pilots, 2.0 cuttaway. Plugs are border line dark brown to black and pistons are still washing clean but pyros go into the 1300's on long pulls and even in mid range. Go richer on needles and it will go flat and blubbery rich. Same on pilots when hitting the choke or going richer on fuel screw. Just looking for any ideas because this combo should work great but haven't found the right combo or any one running a setup like this. It could be the Rugland pipes and or these power pacs I put in the carbs. Any info would be greatly apprecitated. Hate to give up now on it.

I had a engine-tech 770 for a few years and had the best luck with cpi 800twin pipes. I was never real impressed with this big bore. Check your piston wash as aluminum melts at 1220...

770

Xring that is what I am confused about running that hot but if I go richer the plugs get darker and it gets blurby so I know the wash and plugs are not lying to me. I am wondering if I am getting false readings because of the rich condition. I basically had to start over this year because my heads were way too tight. I sent them up to Art at Engine Tech and he re-domed them to live. It would go down on long runs on race gas. I am also wondering if this kit was a race kit and not the trail kit that I was told. My probes may also be too close and I know the probles are only a guage but they are also no good if your readings are so high. This is was I get for piecing a sled together with used parts but I knew that going in. I am ready to get an EFI and ride more but I don't want to give up on it with all the time I have put in it so far.

Pure aluminium melts at 1200 I'm sure the alloys they use in the motor are much higher... I have set my warning on my egt at 1350 and haven't melted anything yet. :face-icon-small-hap Thats just what I determined to set it at from the piston wash. This is on an 01 polaris 800 with SLP twins though...

I'm running an ET 770 with a set of mikunis from a 2000 800 rmk. Art bored them to 41.5 mm for me. I'm using the stock '04 800 rmk needles, DGN6-57 #3, a .7 air jet and the fuel screws out 1 1/2 turns. Mj are 370 mag and 360 pto @ 5000' to 6000' 0C to about-5C No bog whatsoever, pulls hard from any rpm. I'm running this in a '98 700 rmk with a 159 x 2.4 polaris series 4 track and I can break it loose at anything under 20 mph. I tried the needles in #2 but was to lean, mj's also are borderline, any colder or lower and I would definately have to jet up. Hope this helps.

edit: Should also say I'm running 25% av/75% premium and Art cut a stock '97 head to 14/1 for this.

Jay thanks for the info above. I am using the 9DFH10-57 needles in number 2.5 stock bore same carbs you have which seems to be pretty good in mid range. Which pipes are you running? I think that I need to pull the power pacs out of the carbs and get the pilots right first. You are suppose to go up on pilots with these installed. I did have 55's in it but went back to 45's last week. Art took my heads back to about 12.5/1 so premium and Torco Accelerator is all I need for fuel now. Based on my plugs my mains should go down one more to 540's and that should be good too 0 f since last weekend we were in the high teens. I broke every rule when I built this thing and did way too many changes without ever owning a Polaris and or ever driving a modded one. Did alot of research though and so far this has been my only problem beside the head issue. Just curious as to what weghts people came up with after building one of these sleds. I came in at 507 empty with the stock hood. Found titanium jack shaft and drive shafts for it, light weight rack, radius rods, spindles, trailing arms, light weight brake rotor, drop and rolled chain case per Fabcraft, Extralight rear skid, 159 2" ported, big wheel rear, SLP front arm relocation on rear skid, Van Amburg tunnel, high top light weight seat, 800 team clutch primary and Team secondary. I cut every bolt to length so they don't extend past the nut that droped over ten pounds when I weighed them. I know the hood would drop 30 plus pounds alone but I like having a hood for storage and my guages. Thanks for the help guys I like working on this old girl just don't have alot of sprare time any more with two young kids. I put in alot of late nights just before my 5 year old was born. Here are a couple of pics of what I spend most of my time working on. These old girls are high maintenace but fun to ride at Vintage rides!!

Jim

Forgot to mention the pipes, they are twin psi end dumps. I'm running 45 p jets. I like this sled but it has it's drawbacks, it's way to heavy, doesn't ride or steer like a newer one but it's fun in it's own way. Also it's all I can afford.:face-icon-small-hap

its a good motor, make sure you run race fuel

770

Update on my low end issue. Two week ago before the snow left I changed the air jets back to .8's and it helped a little bit. Then I took out the power packs and all is good now. Apparently this motor doesn't like them since I have used them in other motors I took it for granted. Now it transitions like it should. Also jetted down too 540's and am still a little rich on the top end yet. Had to do the same on another mod I had and not even pay any attention to the pyros till the plugs looked good. I may just have been so rich that the flame was alot of un-used fuel. Will see if we get one last cold snap or next year.

Jim