AJP start - vyřešeno

Product reviewed

The review focuses on an AJP PR7 (2018 model), specifically its cold-start behavior on older units using a Delphi control unit. The reviewer tests a simple wiring modification using a standard automotive relay to improve cold starting by feeding the fuel pump directly from the battery.

Key features / what was changed

• Original issue: Older AJP PR7 units (notably the 2018 model) have cold-start problems, especially after the bike sits overnight in cold temperatures.
• Modification: Install a single standard car relay so the fuel pump receives full battery current directly.
  • Battery + → fuel pump through the relay
  • Fuel pump ground → direct to battery −
  • Existing wiring is repurposed to switch the relay (relay terminals 86 and 85 are mentioned)
• Other changes for the test/sale prep: Nothing else about the bike is described as changing for the experiment besides being tuned/serviced and having filters/mufflers added (not detailed), mainly because it would be sold.

User experience / results (cold starts)

• The bike was parked outside all night, in cold conditions (the description notes that even if daytime was hot, nights were cold).
• After relay installation:
  • When the start is activated, the relay clicks and the fuel pump begins flowing.
  • The reviewer reports that pump/pressure behavior suggests the pump gets much stronger voltage/current from the battery.
  • The fuel filter/pump area appears more flooded than usual, which the reviewer attributes to the stronger pump drive current.
  • Overall cold-start performance improves substantially compared to earlier attempts.
• Remaining issue: battery weakness
  • The bike still shows signs of weak battery condition (“battery old” / click, click).
  • Even with the relay, the reviewer initially needed help:
    • A donor PR7 (2025) and jump leads/jump-power (jump-lead/flashlight setup) were used to assist.
  • The reviewer believes the problem is not fully solved by “jump-power” alone, and suggests the main lingering factor is battery age/condition.

Pros (as stated)

• Simple fix: “One relay is enough.”
• Improves fuel delivery during cold start:
  • Stronger pump current
  • More fuel flooding at the filter/pump area than usual
  • Faster/stronger fueling behavior during attempts
• Low complexity: No major electrical/electronic complexity needed versus “Mambo jumbo tricks” (the reviewer’s phrase) such as repeated switching/stands/ignition tricks.
• Confidence boost: The reviewer expected touching the electrical system to be difficult, but found the result works and isn’t overly complicated.

Cons / downsides

• Battery still matters:
  • Cold-start struggles weren’t fully eliminated because the battery is old.
  • The reviewer explicitly indicates the bike may still require charging or a modern battery despite the relay mod.
• Minor risk/cost:
  • There’s mention of possibly ruining the flashlight/jump setup during attempts (a practical nuisance during testing).
• Wiring improvement suggestion:
  • The reviewer suggests the wiring could have been insulated better (“could have isolated it a little better”), not as a major failure, but as an improvement.

Comparisons made

• Compared to earlier cold-start methods:
  • The reviewer criticizes prior “tricks” (stand/gas/ignition switching) as unnecessary and/or less effective.
• Older vs newer model context:
  • The reviewer notes the 2025+ model was solved already by Portuguese builders (cold-start issue reportedly fixed in newer units).
  • This test targets a 2018 unit, implying the relay modification is mainly for owners without the newer fix.
• Starter pack/jump leads vs relay mod:
  • A starter pack helped the bike rev more, but it did not start immediately.
  • The relay improves fuel delivery, but battery weakness can still prevent reliable starting.

Unique points mentioned

1. The 2018 AJP PR7 has a known cold-start problem on older Delphi control unit setups.
2. Cold ambient overnight parking is a key factor in the failure behavior.
3. The reviewer avoided riding in fall due to unreliable cold starts.
4. The tested fix is a single car relay that powers the fuel pump directly from the battery.
5. Relay concept/wiring:
   • • to fuel pump via relay
   • − directly to fuel pump
   • Original control wires switch the relay (terminals 86/85 mentioned)
6. More current/voltage reaches the pump, causing stronger fueling behavior.
7. The fuel filter/pump area appears more flooded than normal (attributed to stronger pump current).
8. Even with the relay, battery condition can still cause problems (“battery old”, “click click”).
9. Jump leads/starter pack are used as backup; the relay isn’t sufficient if the battery is too weak.
10. The reviewer frames this as useful for users with poor cold starts who don’t have a 2025 or newer model.
11. The reviewer admits they expected fully hassle-free results, but battery condition still needed attention.
12. Štěpán is thanked for suggesting placing the relay earlier.
13. Some editing was not used for believability when handling the jump lead situation (practical note).
14. The reviewer says this is likely the final video in their cold-start series for this topic.
15. The bike is being prepped for sale (tune-up, filters, mufflers).

Speaker contributions

• Primary speaker (reviewer):
  • Explains the cold-start problem, implements and describes the relay wiring modification, and reports the starting results.
  • Offers the “battery is old” explanation and the observation about increased flooding.
• Mentioned commenters / others:
  • Štěpán: recommended the relay approach early (credited in comments).
  • A commenter suggesting “buy a new battery”: mentioned as advice; the reviewer partially rejects it as a complete solution, discussing relay vs. battery condition.
  • Portuguese guys / PR7 2025 context: described as having solved the issue already on newer units.

Overall verdict / recommendation

For older AJP PR7 (2018) cold-start problems, the reviewer’s main takeaway is that using a single standard car relay to power the fuel pump directly from the battery is an effective low-complexity fix—especially for improving fuel delivery during cold starts.

That said, the reviewer emphasizes that a weak/old battery can still prevent reliable starting. So the relay is best seen as a solution to pump control/current delivery, not a guaranteed replacement for proper battery health.