Are all primer/purge bulbs 'not' a must for an engine to run prop

loger_gwSeptember 1, 2011

1. Are all primer/purge bulbs not a must for an engine to run properly "vs" starting? On all 4 cycle I would say "No" but I'm not sure on all 2 cycles.

2. I recently replaced the fuel line and bulb on a Ryobi 770r 32cc. The theory of how the priming worked and how the lines were connected, basically made me think it had to be in the running system. But! with the primer/purge pulling and pushing action, I can feel it is by-passed after starting.

3. The worst part was some of the line was completely missing vs me getting a visual Pic or real pics showing the fuel line diagram. On-line I found good info listed in 3 steps and theory and a video showing the steps. Listed below and at the addresses. It Did Start Easy As Promised. loger

How to replace primer bulb:

I found a fuel line connection diagram for a model 770r. It had basically the same connections. The pattern is:

1. Top of carb to primer bulb suction

2. Fuel tank connection (the one with the filter on inside of tank) to bottom of carb

3. Primer bulb discharge to fuel tank connection

The primer bulb pulls fuel from the carb and pumps it back into the fuel tank. This causes a vacuum in the carb that pulls fuel through the carb from the fuel line connected to the filtered fuel connection.

I connected this up and my Ryobi 790r weedeater started right up.

Video & Info:

This is a different model # Ryobi trimmer but I feel the connections and processes are good. I know the processes are good from what I learned trial and error.

Thank you for reporting this comment. Undo

I didn't want to drive 10 miles to buy a primer bulb for a Homelite sx 125 2 cycle string trimmer so I used the outside of the bulb mounting plate as a pattern to cut a gasket.
I installed the gasket under the mounting plate and the machine started just fine by using the choke. I have since replaced the Homelite with an Echo SRM-210 which is a much better and easier to use string trimmer.

    Bookmark   September 4, 2011 at 9:58AM
Thank you for reporting this comment. Undo

Thanks for the reply Ray! I tried the same experiment on my old Green Machine trimmer (#030348, 22.5 cc)while waiting for a bulb. I sealed the bulb's circuit with thick plastic and the bulb's retainer. The trimmer would start and idle easily but w/n produce good RPM until I added the bulb.

From your results of your trimmer working and mine w/n, I feel it depends on the system and possibly if the system is sealed or not. The Bottom Line Question! When the bulb is cracked, will the engine run properly (using an alternate primer to start)? loger

    Bookmark   September 4, 2011 at 1:02PM
Thank you for reporting this comment. Undo

I did not seal off the circuity. The net result was just to produce a seal to prevent fuel leakage when running.

    Bookmark   September 4, 2011 at 2:03PM
Sign Up to comment
More Discussions
Kohler K181 valve clearance
The engine would run perfect for maybe 30-45 minutes,...
Poulan Pro rear tine tiller, burnt valve??
I have a 6.5 Intec Briggs on my tiller, which is 10...
Craftsman Snow Blower - Drive problem
During our big storm last week i noticed I started...
Troy Bilt Pony Tiller
I have a Troy Bilt Pony Tiller with a 5 HP Briggs and...
Older Troy Built Tiller Model ID
Trying to indentify model number of my unit. It is...
© 2015 Houzz Inc. Houzz® The new way to design your home™