Helix 150 engine swap, single seat conversion

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Kaptain Krunch

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Hey folks,

Been out of the Go cart game for a while. Life, business, and house projects have taken over. last summer i impulsively picked up a Chinese gy6 go cart/buggy with a blown engine for $100, with absolutely no plan for it. I'm finally digging in, and i believe i have a rough idea of what the final product will look like.

The TO-DO list:

- Center steering wheel, remove bench seat install single bucket
- Modify front suspension to accept larger tires, front brakes
- swap out engine for something more powerful

I intend on leaving the original rear swing arm and axle. I'm not fond of swing arm mounted engines, due to the massive amount of unsprung weight, however it will have to do for now.

For the power-plant i THINK i'll be using a polaris trailboss 250 engine. It is a 2 cycle oil injected, air cooled unit. Electric start. I also have a matching FNR transmission and CVT from the same machine. While i would like more power, this seems like the lightest option (see unsprung weight).

Other engine options
- vanguard 16hp v twin (heavy)
- 400CC kawasaki motorcycle engine (heavy)
- 250cc polaris snowmobile engine (similar to trailboss, less power, no electric start)
- 400cc yamaha snowmobile engine (no electric start)


Progress will likely be slow, But i will keep this page updated as i go.

Pictures attached are the trail boss engine and transmission, and chassis.
 

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Kaptain Krunch

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Ultimately i'd like the bike engine, but im not sure if i want to commit to that massive of a project just yet. Id have to build an IRS system (trailing or a arm), as im not willing to deal with that much unsprung weight on a swing arm.

However, i mounted the transmission friday and am running out of space quick, so i may have to go that route. i'm going to spend some time on it tomorrow afternoon. pics to come.
 

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Engine and transmission are mounted and tacked in place. Transmission will need a few more mounts. engine will get a few more braces. I decided on the starlite 250 motor rather than the trail boss due to size. the starlite has smaller cooling fins due to having a cooling fan.

They are both EC25 fuji motors, the trail boss motor turns out to be lower revving (5300 vs 6300). The trail boss motor made more hp, but the starlite lacks a tuned pipe. My hopes are that i can either use the tuned pipe from the trail boss, or build my own to better suit. I have not measured port heigh or diameter of both engines, but they do have the same bore and stroke. Modified trail boss's can make upwards or 35hp. Id be content with 30.

Im using the trail boss secondary clutch, and the starlite primary clutch. I installed new buttons in the secondary, and used the spring from the starlite secondary in the trail boss. The helix angles are the same. Only difference is the trail boss uses a 1 3/16 belt, whereas the starlite uses a 1 1/4...should be fine.

Going to order chain and sprockets soon, stock gearing was 12/42 with 22" tires, i have a set of 24" mudlites i plan on using, will likely go with a 45t, and keep the 12 up top.



 

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Burned in engine and transmission mounts, out of gas so using some ugly flux core wire (but it was free!). Clutch is aligned with the proper 5/8 offset polaris specifies. Brand new dayco belt install. I mounted the sprocket to the axle, kind of funky but spins true.

I removed some old mounts and brackets on the swing arm, and the battery box. Exhaust, chain, and brakes are next on the hit list.




 

Kaptain Krunch

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So i've made progress despite the lack of pictures. I use my phone for spotify in the shop, and always forget to take them.

What has been done:

Exhaust made, would like to do an expansion chamber eventually.
Fuel and oil tanks mounted
New brake pads, freed up master cylinder. SHE STOPS!
Rigged up throttle and kill switch for a temporary test.
Chain is on, need to make a tensioner.

It runs and drives fairly well! having some running issues, due to jetting i believe. It was originally set up with a fuel pump, and the current setup is gravity feed. The brakes seem inadequate for the speed it is capable of now, i think the caliper is sufficient but i will likely upgrade the master cylinder.

 
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