1980 Sport -Farm Rescue, Need help!

[sparksman]

Hi and welcome to mightyram. This find is a gem in the rough. The Sport 50's are pretty cool and even though the tin worm has had a feed on it, it is complete and straight. The spring mod on the secondary isn't a great idea as the Mikuni is internally vacuum metered. It will run but not properly. The secondary vac actuator can be removed and replaced without removing the carb (with a bit of manipulation). If it will idle, check your timing and rpm. Check the adjustment on the throttle cable to make sure it isn't loading the throttle linkages, then check the throttle stop screw. Wind it out all the way and check the rpm @ idle - if it's idling high or low recheck the timing (the primary throttle linkage should only be resting on the throttle stop screw and not being loaded by it). The air/fuel mixture screw is approx 1 1/2 - 1 3/4 turns out from being wound in all the way first. There is a fast idle adjust screw on the underside of the primary throttle linkage - this needs to be set from a cold start. Wind it in/out until you get a cold idle of approx 1200 rpm (it's a screw with a small captive spring sandwiched in it - do not wind it all the way out or the spring and screw will fly into the abyss of the engine bay ne'er to be seen again + it is no easy feat to get them back together). This should hopefully be a helpful start. You may need to adjust the choke cam gear and depending on the model Mikuni may only need a couple of bracket screws removed or worst case a mini die grinder to take the top off some retaining studs. Keep us posted on your progress, use the search function and ask questions. The Mikuni is a tricky thing to work on but isn't completely hopeless (there's always the Weber 32/36 upgrade that has proven itself more than worthwhile as an alternative)

Thanks for the reply! I have the secondary vac chamber off, i watched a video on how to use the spring to get the secondaries to open. I wont spend the $100 on a new chamber. Maybe if i can find one in a wrecking yard to pocket lol, i just need it drive able at any speed for now. The truck did idle, but i had to hold the choke butterfly by hand or it would die. So choke is 100% in need of adjustment. When it is warm it will idle for a few min before dying, any fuel instantly kills it. If i wiggle the throttle and work up the revs it will actually rev up and sounds half way decent. I dont have the carb or truck in front of me, can you run a spring and loop the vac lines, or plug them up? As for timing i was able to adjust the timing after i got idleing, 7 deg BTC. lol... well its at 7 degrees... just ATC. The dumb marks on the engine were unreadable so i went the wrong way. So i pulled the carb off and found out the egr was stuck at mid way anyhow. Wasnt allowing the throttle to operate correctly. I also read you need to take the vac lines off the dizzy before setting the timing. I didnt, so im sure that probably effected it in a negative way.

This is the first carb vehicle ive ever worked on, not counting my motorcycle. Ive rebuilt engines, and built my current car I drive from a bare shell. There is a learning curve to this old technology, and this seems like a PITA of a carb to learn on too. This truck is 9 years older then i am, I was just explaining to my father whom i enlisted for help working on this. To me, this would be like him working on a late 40's truck lol. First time ive touched a vehicle with glass fuses.

Honestly as much as id like to clean this truck up and make it super nice. I dont see me dropping a ton of money into it in the foreseeable future. Let alone a whole new weber carb, this truck is going to be my budget build. I have too many other projects at the moment. Im building a flat-bed utility trailer from a old camper trailer. Just finished my boat overhaul. Still working on minor things on my street legal dirtbike, and my car needs some attention before the turbo goes on. I only got the truck because it was 100% free. Im $30 into parts so far, so as it sits its my $30 truck. Long story short im spread to thin to actual give the truck the attention it really needs other then basic tune up. Having two other means of transportation makes this more or less a toy then necessity. I plan on using on the property to haul brush, and what ever around 99% of the time. Maybe use to go hunting, since my car is low and wont do gravel.

I will be cleaning it up, and want to make it reliable. This little truck has grown on me, the yellow and rainbow stripes is such a bad color scheme its actually awesome. A very 70's retro vibe i get from it, which makes me want to see it on the road again. Its like a piece of rusty art haha. Here is a pic of the carb after i pulled it off. What are the two screws in he center? Whats the factory twist count for those? Not 100% sure, but may have been tampered with since i know for a fact im not the first to pull the carb off. There were truck parts in the back of the cab when i brought home, so i know someone was working on it before it sat.

Looks like the one off CL with buckets and a 2.6 from Salem. Is it?

Nope, this was in Yacolt WA, 40 min north of vancouver, other side of battleground.